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Wedged Mortise and Tenon

Wedged Mortise and Tenon

This joint will never loosen!

By Tom Caspar

 

Tap, tap, tap. The wedges go home, the glue squeezes out and a big smile lights up your face. “This joint isn’t coming apart for a hundred years,” you say. “It’s as solid as a rock!”

Making a wedged mortise-andtenon joint is richly rewarding. Once you understand how it works (see "How the Joint Works," right), you can’t help but admire the joint’s elegant simplicity. It also sends a message. A wedged joint says to one and all, “This was made by a skilled woodworker.”

Where could you use a wedged joint? It’s a candidate for any joint that receives a lot of stress. A table base such as the one shown here, is a good example. Pushing or leaning on the table might slowly force a standard joint apart, but wedges keep this joint locked together.

The wedged mortise-and-tenon joint isn’t difficult to make, but you should have some experience making standard mortise-and-tenon joints before tackling it.

 

Tools required

To make this joint, you’ll need a tablesaw, drill press, plunge router, chisel and a bandsaw. If your mortise’s width is 5/8" or more, like the mortise I made, you’ll need a 1/2" dia. top-bearing flush-trim bit. If the mortise is more than 3/4" deep, you’ll need a bottom-bearing flush-trim bit (see Source, below). For a mortise less than 5/8" wide, you’ll need a straight router bit and a fence or jig for your plunge router.

 

Rout the mortise

Before you begin your project, make a prototype joint (see “Designing Your Wedged Joint,” right).

It’s good practice to start with the mortise for any type of mortise-and-tenon joint. It’s easier to fine-tune a tenon to fit a mortise than the other way around.

This is a through-mortise, meaning it goes all the way through the workpiece. My favorite way to make a fairly large one is to remove most of the waste on the drill press and then use a plunge router and template (Photo 1). This method works particularly well in thick stock, because it makes a mortise with absolutely straight walls. That’s important for appearance’s sake in a through joint, because you can clearly see from the outside how well the mortise and tenon fit together.

Make the template from plywood or solid wood by gluing four pieces together. The inner two pieces are the exact width of the mortise, but their overall length is unimportant. The outer pieces must be long enough to allow room for clamps. Space the inner pieces apart by the length of the mortise.

Before you start routing, use the template to draw the mortise on the workpiece. Drill out most of the waste using a Forstner bit that’s 1/16" to 1/8" smaller than the mortise’s width. Make overlapping holes to remove as much wood as possible. Rout the mortise (Photo 2).

 

Taper the mortise

Tapering the ends of the mortise requires a razor-sharp chisel; there’s no practical way to do it with a router. You must use a chisel to square the ends of a routed mortise anyway; so tapering isn’t that much extra work.

Make a 1-1/2" to 2" thick block to guide your chisel. Cut one end square. Cut the other end at the angle you’ve chosen for tapering the mortise and wedges. I’ve found that a 3-degree angle works well.

Use the guide block’s right-angle end to square the back of the mortise. Chop about one-fourth of the mortise’s depth. Turn the workpiece over and position the block a short distance away from the end of the mortise (Photo 3). The exact distance depends on the mortise’s depth. You’ll want the taper to extend approximately three-fourths of the way down the mortise. On a 3-degree taper, shifting the block 1/16" from the mortise’s ends results in a taper about 1" deep.

 

Make the tenon

Make the tenon any way you want. I use a tablesaw tenoning jig to cut its cheeks, a bandsaw equipped with a fence to rip its top and bottom sides and a tablesaw’s miter gauge to cut all four shoulders. The tenon’s length is up to you; it can be flush or stand proud of the joint.

Fit the tenon to the back, untapered side of the mortise. It should be no more than a paper thickness smaller than the opening. If your tenon stands proud, chamfer its end using a block plane or file.

The next two steps are unique to this joint: making the strain-relief holes and sawing kerfs for the wedges. Start by marking and drilling the holes (Photo 4). Their location and diameter determine the flexible strips’ thickness. In most woods, such as the white oak I’m using here, I drill 1/4" dia. holes centered 1/4" from the edge. This makes the bending strip a flexible 1/8" thick. Holes that are only 1/8" are commonly used for this joint, too, for types of wood that bend easily, such as maple and ash.

For the saw kerfs, draw lines that connect the holes to the tenon’s end. Traditionally, the kerfs go to a hole’s center, but I aim for the hole’s inside edge (Photo 5). Looking headon at the completed joint, I believe this divides the tenon into more pleasing proportions.

 

Saw the wedges

Make wedges using the tablesaw (Photo 6). This method allows you to cut a precise angle and fine-tune each wedge’s thickness. Make a wedge blank from straight-grained wood. I prefer one that contrasts in color from the tenon. Make the blank about 3/4" thick and as wide as the mortise.

Tilt the blade to the guide block’s angle. Here, it’s 3 degrees. Raise the blade to make wedges that are about 1" longer than the tenon.

For a trial cut, position the stop block so the thin end of the wedge is the same thickness as the tenon’s kerfs. Clamp the blank to a tall fence using a wooden handscrew. (A wooden clamp protects your blade from damage if you accidentally place the clamp too low.) Flip the blank around to cut a second wedge. Remove the blank and crosscut the wedges by hand or on the bandsaw. File chamfers all the way around the wedges’ thin ends.

 

Test the wedges’ fit

Push the tenon all the way through the mortise—without glue, of course. Tap in the wedges, but not too hard (Photo 7). If they’re too skinny, cut them shorter or adjust the stop block and saw new ones. If your wedges become stuck, pull them out using locking pliers. The wedges should go in as far as possible but not be so long that they hit bottom before fully spreading the tenon. Marking the bandsaw kerf’s length on each wedge will help you prevent this problem.

 

Assemble the joint

When everything is ready to go together, you only have to put glue on the mortise’s long sides and the tenon’s cheeks. Clamp the joint so the tenon’s shoulders are tight to the mortise. Then brush glue into the saw kerfs and the mortise’s tapered spaces. Tap in both wedges and clean up the glue squeeze-out. Saw off the wedge’s excess length after the glue dries. Use a file or low-angle block plane to level the wedges flush to the tenon.

Click any image to view a larger version.

How the Joint Works

Here’s a cutaway view of a wedged mortise-and-tenon joint. Driving in the wedges forces the tenon to flare into a fan or dovetail shape. The mortise is tapered to match the angle of each wedge. Like a dovetail, this joint can’t pull apart after the wedges go home.

This tenon has two unusual features: saw kerfs that create flexible strips and holes that disperse the strain that the wedges create. The wedges cause the strips to bend; the holes prevent the bend from splitting the rail.


1. Make the mortise before you cut the tenon. I use a shop-made template, a drill press, plunge router and two flush-trim bits to make large throughmortises (Photo 2). The hole in the template is the exact size of the mortise.


2. Here’s a cross section of the mortise in various stages of completion. You make it in four steps: 1. Drill out most of the waste. 2. Follow the template with a short top-bearing flushtrim bit. 3. Using the same bit, remove the template and rout deeper. 4. Flip the workpiece and finish the mortise with a bottom-bearing flush-trim bit.


3. Using an angled guide block and chisel, taper the mortise’s ends into a flared shape. The taper leans 3 degrees from square. Make the taper about three-fourths the depth of the mortise. Turn the mortise over and square the remaining corners.


Designing Your Wedged Joint

Each part of a wedged joint must often be tailored to fit the joint’s size, intended strength and type of wood. Make a prototype following these steps:

1. Substitute a notch made with a dado set for the mortise (see “How the Joint Works,” page 2). Taper both of the notch’s sides by angling the miter gauge.

2. Make a full-size tenon. Observe how well the flexible strips bend. You may be able to use smaller strain-relief holes or no holes at all.

3. Experiment with the notch’s angle. The wider the taper, the stronger the joint. My taper is 3 degrees, but you can increase it up to 8 degrees.

4. Test the bend. My flexible strips are only 1/8" thick opposite the strain-relief hole; so they bend easily. Depending on the wood, this thickness can be increased to 1/4" or so to improve the joint’s appearance.


4. Cut a tenon to fit tightly into the back of the mortise, where there’s no taper. On the tenon, draw a centerline directly opposite the point where the mortise begins to taper outward. Drill two strain-relief holes all the way through the tenon.


5. Saw kerfs in the tenon to receive the wedges. This creates strips that can flex without breaking. I aim for the inner edge of the hole so that the kerfs don’t end up too close to the tenon’s edges.


6. Cut extra-long wedges on the tablesaw. Tilt the blade 3 degrees—the same angle as the guide block you used to taper the mortise. Crosscut the wedges from the blank with a bandsaw.

Caution: You must remove the blade’s guard for this cut. Be careful.


7. Test-fit the wedges without glue. You have to get their thickness just right to completely flare the tenon before the wedges hit bottom. Adjust the tablesaw setup until the wedges are the right size. You’re ready for gluing.

 

Sources

Note: Product availability and prices are subject to change.

MLCS Woodworking, mlcswoodworking.com, 800-533-9298, 1/2" Pattern/ Flush-Trim Bit, 1/4" shank, #16509; 1/2" Flush-Trim Bit, 1/2" shank, #17803.


This story originally appeared in American Woodworker July 2006, issue #122.

July 2006, issue #122

Purchase this back issue.

 

 

Thermally Modified Wood

Thermally Modified Wood

A remarkable drying process gives wood a new character.

By Chad Stanton

Some day, you'll be able to build an outdoor project with a new kind of wood, grown right here in America, which resists decay, stays absolutely flat and is totally free of chemicals. Sound too good to be true? Well, that day isn’t way off in the future— this wood is here, right now.

It’s called thermally modified wood, or TMW for short. I’ll go into the details later, but basically TMW is wood that’s been dried at a really high temperature. This turns it brown all the way through—like a chocolate cookie. But it’s a cookie that mold and fungus can’t digest. TMW won’t rot.

Any species of wood can be turned into TMW—hardwood or softwood.

 

Origins of TMW

Credit goes to Finland for figuring out how to make TMW. Actually, TMW’s rot resistance was an accidental discovery. Back in the early '90s, Finnish scientists were experimenting with a drying process that would make wood more dimensionally stable—that is, free from cupping, bowing and twisting. Good luck with that, you might think. But they hit the jackpot. Not only did they achieve their goal, but they found that the process made the wood rot-resistant, too.

Of course, baking the wood in a super-hot kiln changes it in other ways, too, not all of which are desirable. More on that below.

For a few years, TMW was an exclusively Scandinavian product. Today, a few American companies have licensed the process and are busy converting domestic woods into TMW.

 

How TMW is made

Making TMW is a complicated, four-step process. To start off, the untreated lumber is dimensioned at the sawmill. Then it’s brought to the kiln and the first step begins: slowly heating the wood to 212 degrees. In the second step, the wood is preconditioned by drying it to nearly 0% MC (moisture content). This wood resists decay, but it’s totally free of chemicals.

Now it’s ready for the crucial third step, where the temperature of the wood is raised to 374-482 degrees for several hours. At this high temperature the natural sugars in the wood are converted into substances that all the agents of rot—insects, mold and fungus—cannot eat. In the final step, the wood is cooled and some moisture is restored, bringing it up to around 6% to 7% MC.

 

Properties of TMW

I first heard about TMW from a friend who’s in the deck-building business. He buys thermally modified Southern yellow pine from PureWood, a company based in North Carolina (for more information, visit purewoodproducts.com). Their 2x6 lumber costs about $2.50 per lineal foot. I used some of that wood to build a large picnic table. Here’s what I’ve learned.

Color and smell. The TMW process darkens the wood all the way through to a cocoa-brown color. If left unfinished outdoors and exposed to sunlight, it will turn gray. TMW has a pleasant smell when you cut it—like toasted marshmallows.

Stability. TMW planks are exceptionally straight and flat. I resawed some wood into thinner pieces and they didn’t warp one bit. That’s a rare experience with any wood—and a welcome one.

• Strength. The drying process seems to make the wood more brittle. It splits and splinters more easily than wood of the same species that’s been kiln-dried. TMW is not recommended for use as joists and posts.

• Dust. Sawing and routing TMW creates very fine dust, like working MDF. It’s a good idea to wear a mask.

• Planing and jointing. No problem. Freshly machined surfaces take glue well, too. Old surfaces should be sanded or milled before gluing.

• Dimensions. The TMW I used was slightly thinner and narrower than standard dimensional lumber. Check before you buy.

 

The bottom line

Like any wood, TMW has its pros and cons. But it’s amazing stuff, and I hope it catches on.



This story originally appeared in American Woodworker June/July 2011, issue #154.

June/July 2011, issue #154

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Handles for Turning Tools

Handles for Turning Tools

Customize their fit for comfort and performance.

By Alan Lacer


Decades ago, woodturning tools came without handles, and turners would simply fashion their own. This makes perfect sense, because a handle that fi ts and feels “right” gives a turner confi dence. And who better to custom-fi t the handle than the person who’ll use the tool?

Turning and installing your own handles is a great exercise in designing, turning to fairly tight tolerances, and drilling wood on the lathe. To get started, you can buy tools unhandled (still an option) or remove their commercial handles (really easy).

 

Use strong, dry wood

Select stock with straight grain, especially for the tool end of the handle (use the strongest grain orientation for this critical area). Traditional hardwoods, many exotic woods, and even local woods that you harvest and dry yourself are all good options. Do not use weak woods such as pine, poplar, butternut, willow, spruce and fir.

Make sure the wood is dry. If you have any doubt about the moisture content, let the handle stabilize for several days (or longer) after roughturning and drilling the initial hole.

I make each handle unique, by using diff erent woods and fi nish colors, so that I can immediately identify each tool. I normally start with stock that’s 1-3/4" to 2" square (Photo 1). The length of the blank depends on a number of factors, including personal preferance and the tool itself. Figure A (below) lists handle lengths that work well for me. It’s always better to make a handle too long, rather than too short.

 

Ferrule stock

Every woodturning tool handle must have a metal ferrule to reinforce the joint between the handle and the tool’s shank, or “tang” (Photo 2). Hardware stores and salvage yards are good sources for ferrule stock. Copper couplings (used to join copper pipe and tubing) are some of the best. They’re available in a variety of diameters and each one can be cut in half to make two ferrules. Choose a diameter that allows plenty of wood between the tool’s shank and the ferrule, usually at least 1/4"–if there’s any question, go with a larger diameter.

 

Make a handle

1. The fi rst step is to drill a 3/8" dia. x 3/4" deep pilot hole for the tang in the blank (Photo 3). Note: If the tang is smaller than 3/8", match the pilot hole’s diameter with the tang. The end you choose for mounting the tang should have straight grain and be free of checks and knots. Clamp the blank in a vise and use a hand-held drill.

2. Install a live center with a cone in the tailstock (see Sources, below). The cone will automatically center the pilot hole when the blank is mounted on the lathe. If you don’t have a cone-type live center, turn a tapered piece of wood to fi t into the blank’s pilot hole and protrude about 1/2" beyond it. When you mount the blank, center the live center’s point on the protruding end.

3. Turn the ferrule end–or the entire blank–to round, using a spindle roughing gouge.

4. Turn a tenon on the end to match the ferrule’s length and inside diameter–go for a driven-on fi t. Slightly taper the tenon’s end to help get the ferrule started. Drive on the ferrule, factory end fi rst, all the way to the tenon's shoulder (Photo 4). This orients the ferrule’s rough-cut end with the end of the tenon. Turn down this rough edge after reinstalling the blank on the lathe. If the edge is very rough, use a mill fi le, off the lathe.

5. For safety, turn a bulb over the part of the handle that will house the tang (Photo 5). This provides maximum strength in the event of a catch or dig-in.

6. Turn the blank to a diameter slightly larger than fi nal size. Then use a detail/spindle gouge to round the back end of the handle.

7. Turn the gripping area of the handle into a shape that you like (Photo 6). Be sure to test the grip with the hand that you will use to control the tool. As the gripping area nears perfection, shape the transition to the bulb to create the optimal feel and balance, but beware of making any portion too thin.

8. Finish-sand the handle and ferrule to 150 grit, with the lathe running. Turn off the lathe and sand with the grain to fi nish the job.

9. Remove the tool rest to drill the tang hole (Photo 7). For round-tang tools, the hole’s depth should be one fourth to one third of the tool’s length. For fl at-tang tools, the hole should house the entire tang—almost to the tool’s shoulder. Mount a Jacobstype drill chuck in the headstock (see Sources) and install an ordinary tapered-point bit (other types of bits won’t enter the pilot hole accurately). Place the handle’s pilot hole against the bit, bring up the tailstock, and lock it. Advance the live center to engage the center hole on the waste end of the tool handle. Put on a fullface shield and set the lathe’s speed between 400 and 600 rpm.

10. Turn on the lathe and check to see that the handle runs true. There should be little or no “ghosting” at the ferrule end. If you see ghosts, stop the lathe and re-center the drill bit in the pilot hole. Once all is running well, take two simultaneous actions to drill the hole: Grasp the spinning handle about halfway back with one hand while cranking the tailstock’s handwheel with the other. Go slowly. If you feel too much resistance, slowly back out of the hole, to remove chips.

11. If the hole must be made larger, to accommodate round tangs that are larger than 3/8" dia., simply repeat the drilling operation, using the appropriate larger taperedpoint bit. Drill stepped holes to accommodate tools with fl at tangs. Drill the small dia. hole the full length of the shank; drill the larger hole only as far as necessary.

12. Finish the back end of the handle off the lathe. Simply cut off the waste with a handsaw and then sand.

13. Set the tool into the handle. This step is critical. I’m a fi rm believer in using epoxy to anchor the tool, so start by pouring a generous amount into the hole. Drive the handle onto the tang (Photo 8). Stop about every quarter of the way to check for alignment—sighting the tool and handle much as you would sight a gun. Look for misalignment left or right and up or down. Tap the tool with the mallet to make corrections.

14. My favorite tool-handle fi nish is the one that comes from hard use: sweat, dirt, wear–and maybe even a little blood. A pure oil fi nish is another option, but any fi lm-forming fi nish (including wipe-on oil-varnishes) will make the handle too slick.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Oneway Manufacturing, oneway.ca, 800-565-7288, Live Center with Cone (#2 Morse taper), #2064.

Packard Woodworks, packardwoodworks.com, 800-683-8876, Jacobs-Style Keyless Chuck (#2 Morse taper) , #111022.


Fig. A: Suggested Handle Lengths


This story originally appeared in American Woodworker August/September 2010, issue #149.

August/September 2010, issue #149

Purchase this back issue.

Click any image to view a larger version.

1. Choose straightgrained hardwood for the handle. Use brass, copper or steel fittings to make the ferrule, which reinforces the joint between the tool and the handle. Copper couplings make excellent ferrules.


2. Turning tool shanks (or “tangs”) are either round or flat. Both types mount in holes bored in the end of the handle. Flat-tang tools require stepped holes to accommodate their tapered shape.


3. Start by drilling a pilot hole for the tool's tang in one end of the handle blank. Then use a cone-shaped center to mount the blank on the lathe, so the pilot hole will be centered when the blank is turned round.


4. Drive on the ferrule after turning a tenon to fit. This ferrule is a copper coupling that's been cut in half. If the tenon is longer than the ferrule, use another ferrule (the other half of the coupling) to drive the first one home.


5. Turn a bulb directly behind the ferrule, to provide the greatest support for the tool’s tang. Most of the handle’s shaping can be done with a spindle roughing gouge.


6. Shape the handle to fit your grip, gradually and selectively reducing the diameter, until it feels just right. Remove the handle often, to check the way it feels in your hand.


7. Install a chuck in the headstock to drill the tang hole. With the lathe running at slow sped, simultaneously grip the handle (so it doesn’t turn) and crank the tailstock, to carefully drive the handle onto the spinning bit.


8. Drive the handle onto the tang, using a waste block to protect the edge. Check frequently to make sure the tool and handle remain properly aligned.

 

Custom-Made Crown Molding

Custom-Made Crown Molding

By John English


Here’s how to make the crown molding for the pantry. It’s all done on the tablesaw. The biggest challenge is figuring out which cut to make when.


1. Make a cove (Cut 1, see lead photo) by running 24-in. or longer boards at 30 degrees to the blade. Guide the board in a jig and apply holddown pressure with a pair of skateboard wheels. Start with a very shallow cut, then raise the blade in 1/16-in. increments until you’ve formed the full cove.

Click any image to view a larger version.


2. Tilt the blade 30 degrees for Cut 2. A handscrew prevents the molding from tipping. Use a zero-clearance insert plate if your plate doesn’t provide adequate support.


3. Keeping the blade at 30 degrees, make Cut 3. The space between the blade and fence is very small. Cut a kerf through a piece of plywood to support the molding stock.


4. For Cut 4, leave the blade at 30 degrees. There should be enough room on your insert plate to support the molding this time.


5. With the blade still tilted at 30 degrees, make Cut 5.


6. Sand the molding with a large block. A can of beets (how fitting for a pantry!) is exactly the right size: just a little bit smaller in diameter than the cove.




This story originally appeared in American Woodworker November 2007, issue #132.

November 2007, issue #132

Purchase this back issue.

 

 

Chemical Ebonizing

Chemical Ebonizing

A sure-fire recipe for turning any wood deep black.

By Richard Tendick


Remember the old slogan, “better living through chemistry”? When it comes to turning wood black—a process called ebonizing—I prefer the chemical approach, which uses solutions made from vinegar, steel wool and tannic acid. Watching them transform an ordinary wood, such as the yellow poplar I’m using here, is magical.

Other methods of ebonizing (dye, ink and paint) use pigments, which can obscure the wood’s grain. The chemical technique leaves an absolutely transparent layer of black. You can still see the wood’s figure and character, particularly after you apply a topcoat.

Woodworkers have long known that rusty, acidic water turns some wood black. Woods that are high in tannic acid, such as oak, walnut and mahogany, work best. The technique I’ll show you adds tannic acid to the wood, so you can ebonize virtually any species. I can’t take credit for this idea, though; it’s been a finisher’s trick for a long time.

 

Mixing the chemicals

The two solutions can be stored and used over and over. The first is more or less liquid rust, which you make with white vinegar and steel wool (Photo 1). For the best results, use Heinz white vinegar and Liberon 4/0 steel wool (see Sources, page 63). This steel wool works well because it doesn’t contain oil, but you could also use regular steel wool and wash out its oil with a detergent. Cover the jar with a lid, then puncture the lid with a small hole to let gas escape. Set the jar aside for a week or so.

Eventually, the pad will dissolve and the formerly clear liquid will turn a dark reddish brown, with a black scum on top. Place a coffee filter in a funnel and pour this gunk through the filter into a new container. Repeat the process two or three times, using new filters, to remove all the solids from the solution.

The second solution, tannic acid, is made with dry powdered tannin (see Sources, below). It’s not expensive, but unfortunately it’s not available in a small quantity. Rather than be stuck with a lifetime’s supply, I’ve shared the surplus with a dozen woodworking friends.

To mix the powder, place 1 heaping tablespoon in a disposable container and add a small amount of water (Photo 2). Stir until the powder forms a paste, then add 1 pint of hot tap water. Transfer the solution to a jar or bottle. It can be used right away.

The next step is to raise the wood’s grain with plain water (Photo 3). This is important to do now, before applying either solution, because you won’t be able to sand the wood during the ebonizing process. After the wood dries, sand off any fuzz you may feel with 280 or 320 grit paper (Photo 4). I usually repeat this process two or three times.

 

Application

It’s clear sailing from here. First, pour a small amount of the tannic acid solution into a shallow container and brush it on your project (Photo 5). Make sure every bit of the surface is covered. Let the wood dry.

Next, pour a small amount of the steel wool and vinegar solution into a separate container. Using a different brush, apply the solution to the wood (Photo 6). Almost immediately, the wood will turn a bluish black. Don’t pour the excess solution back into your original container, as it will be contaminated by the tannic acid. Again, let the wood dry. Finally, apply another coat of tannic acid, using a rag to avoid brush marks (Photo 7). Voila! You’ll get a rich, deep black.

Dispose the surplus tannic acid (it will be contaminated, too), and let the wood dry a day or two. You’re ready to apply a clear finish.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

FinishSupply.com, shellac.net, 707-226-3623, Dry Powdered Tannin, 8 oz.

Highland Woodworking, highlandwoodworking.com, 800-241-6748, Liberon 4/0 Steel Wool, 100g.


This story originally appeared in American Woodworker October/November 2010, issue #150.

October/November 2010, issue #150

Purchase this back issue.

Click any image to view a larger version.

1. Dissolve steel wool in vinegar to make the first of two solutions you’ll need. The pad should completely dissolve in about one week.


2. Make tannic acid for the second solution. Mix dry powdered tannin with a small amount of water to make a paste, then add more water.


3. Raise the grain before you begin the ebonizing process. Wet the wood’s surface with a damp rag or sponge.


4. Sand with fine paper to remove any fibers sticking up from the wood’s surface.


5. Brush on the tannic acid solution and let it dry.


6. Apply the vinegar and steel wool solution. The surface will turn a bluish black right away.


7. Apply more tannic acid with a rag. This turns the wood a deep, transparent black. After it dries, you’re ready for a topcoat.

 

Spalted Wood

Spalted Wood

By Alan Lacer


When wood is captured somewhere between the extremes of being completely sound and fully rotten, it can display magnificent beauty. The discoloration, prominent black lines and changes in texture that occur during the decaying process are known to woodworkers as spalting.

Spalting is a by-product of the rotting process that is carried out by a vast army of stain, mold and decay fungi. They are abundantly present in the air and soil, waiting for favorable conditions and a suitable host. Generally, wood moisture content of at least 25 percent, temperatures from about 40- to 90-degrees F, air and food (especially abundant in sap wood) are what the fungi need. A tree or branch freshly fallen onto a damp forest floor in warm weather is asking for it.

Lighter colored woods offer the best canvas for nature’s graphic work. Hard maple is viewed as the king of spalted woods, although sycamore, persimmon, red and white oak, elm, pecan, birch, buckeye, apple, magnolia, beech, holly, hackberry, box elder and the sapwoods of walnut and cocobolo are favored by woodworkers as well.


Where to find spalted wood

You can purchase spalted wood—usually maple—from specialty lumber and mail order suppliers (see Sources, below). Turning blocks are most easily found, but a few suppliers offer boards when they can get them.

Hunting spalted wood is like panning for gold—lots of searching for that one precious nugget. Logs rotting on the forest floor, dead limbs and entire dead standing trees are excellent sources. You can also hunt for hidden treasure at a community bone yard of removed trees, and don’t overlook the bottom of your old firewood pile.


Make your own spalted wood

Woodworkers commonly use these methods to cause wood to spalt. They will work most effectively if the temperature is kept where the fungi will thrive, between 60- and 80-degrees F. Monitor the spalting progress monthly—the optimal conditions you’ve created can make it happen fast.

• Place a freshly cut log section 2 to 3 ft. long upright on the bare ground. Put a shovel of dirt on the top end and cover it loosely with black plastic.

• Bury a log, freshly sawn green boards or green rough-turned bowls in damp sawdust containing pieces of rotten wood with active fungi. Keep the sawdust moist.

• Use plastic bags or plastic garbage cans to hold short sections of green wood or rough-turned bowls. Adding some soil or rotting sawdust may speed the process, although the fungi already present in the air or on the wood surface is probably enough to get it going. Leave the bags or cans with a small opening to allow for some air exchange.


How to stabilize spalted wood

Remove those things the fungi need to grow, and you’ll stop its progress. One method is to lower the wood’s moisture content.Wood below 25-percent moisture content, when kept in low relative humidity, is not likely to decay or even stain. Accomplish this by air or kiln drying, placing smaller pieces in a microwave or finish turning if the piece was a rough-turned bowl. You can also raise or lower the wood’s temperature. Spalting rarely occurs above 90-degrees F and stops below 32-degrees F. Some turners store blanks in a freezer prior to finish turning. Finally, you can restrict the air—no air, no decay. Logs submerged in water, for example, do not decompose from fungi. Tightly wrapping the wood in several layers of plastic will restrict the air and slow the growth of the fungi.

 

Working properties

If you’re lucky, you’ll catch the spalting at the right time, before the cellular structure of the wood deteriorates, and you’ll be able to work the piece without any trouble. Sometimes, however, the material will have areas that have become soft and punky. These areas have no strength and defy normal woodworking strategies. They will crumble, tear out in chunks or leave a wrinkled appearance when you try to cut or plane them. They refuse to be glued together, and leave you with a cratered, uneven surface when you try to sand. Though not suitable for joinery, these soft areas can often be stiffened enough to finish so the piece of wood can still be used decoratively.

You can saturate soft areas with a liquid hardener. Where the wood is only marginally soft, a spot coat or two of clear shellac or nitrocellulose sanding sealer may harden it sufficiently. A really punky spot will require cyanoacrylate (CA) glue (the thin, watery type) or a product made to stabilize rotten wood. There are a number of them sold as wood hardeners at hardware stores. It may take several generous applications to treat each bad spot. These hardeners are effective, but they have side effects. They fill the wood cells, so surfaces treated with them can’t be glued and oil finishes don’t take well because they can’t penetrate. Solvent-based hardeners and CA glues darken the wood considerably. I like Protective Coatings Petrifier (see Sources, below). It’s a water-based hardener that doesn’t discolor the wood, yet seals and stiffens effectively. It’s an excellent choice for troublesome soft spots.

You should be able to work the stiffened surface with edge tools—make very light cuts—or with abrasives, taking care to provide a firm, flat backing for the sandpaper. Some turners use body grinders or stiffbacked sanding discs and work the piece while it’s spinning on the lathe. For flat lumber, an abrasive planer is an excellent option, followed by a randomorbit or pad sander. If you sand by hand, use a sanding block to give firm support to the paper.

 

Finishing

You are likely to encounter three problems when you finish spalted wood: Splotching, yellowing and excessive darkening. The whiter woods—which usually have the most dramatic examples of spalting—can turn quite yellow with certain finishes, and because the soft areas act like end-grain or even a sponge, splotching or excessive darkening can result unless the piece is sealed first. An effective weapon against splotching is clear, dewaxed shellac used as a sealer. (Spray cans of shellac are thinned and dewaxed.) Cover the entire piece with a thin coat and let it dry. Then recoat dull-looking areas until all surfaces have a uniform sheen. You can use almost any finish as a topcoat over dewaxed shellac after it’s been sanded.

To minimize yellowing and darkening, use a surfacefilm finish like clear shellac or lacquer. Waterborne finishes dry clear and don’t yellow with age. If the piece is primarily decorative and has few, if any, soft areas, clear wax is appropriate.

If you don’t mind the yellowing and darkening, use your favorite oil finish, but be prepared to make many applications to the softer areas. Experience has taught me that an oil-finished spalted piece will appear rather muddy and uneven at first, but will look better as the finish cures, which can take weeks or even months. Some oil finishes (such as General Finishes Sealacell Step 1, see Sources, below) are essentially a thinned, light-colored varnish, and will not yellow as much.

If you are looking for a challenge, and effects that often surpass the wildest woods from the tropics, spalted wood may be your ticket. Each block of wood has its own unique properties that must be judged and worked on its own terms. Use spalted wood and your work will never go unnoticed. Use it well, and you’ll produce a real showstopper.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Flat material suppliers:

Northwest Timber
P.O. Box 1010
Jefferson, OR 97352
541-327-1000


Randel Woods
P.O. Box 96
Randel,WA 98377
360-497-2071


Talarico Hardwoods

RD #3 Box 3268
Mohnton, PA 19540-9339
610-775-0400

 

Bigleaf Maple:

Mount. Cheam Woodworking
8359 Banford Road
Chilliwack, B.C.V20GH3
604-795-9297

 

Turning stock suppliers:

One Good Turn
6064 S. 300 W. #11
Murray, UT 84107
801-266-1578


Choice Woods
833 W. Main St.
Louisville, KY 40202
888-895-7779


Craft Supplies USA

1287 E. 1120 S.
Provo, UT 84606
800-551-8876


Hot Stuff CA Glue
Satellite City, P.O. Box 836
Simi Valley, CA 93062
800-786-0062


P. C. Petrifier
Protective Coatings
221 S. 3rd St.
Allentown, PA 18102
800-220-2103


General Finishes
Sealacell Step 1
P.O. Box 51567
New Berlin,WI 53151
800-888-8286

 

For further reading:

"Sculpting Wood" by Mark
Lindquist, 1986, Worcester, Mass., Davis Publications, 800-533-2847. Mark and his father Mel have been pioneers in working spalted wood and in popularizing its use as a decorative material.

"Understanding Wood" by Bruce Hoadley, 1980, Newtown, Conn., Taunton Press, 800-888-8286.


This story originally appeared in American Woodworker December 1999, issue #77.

December 1999, issue #77

Purchase this back issue.

Click any image to view a larger version.


Cabinet on Stand English oak with spalted bigleaf maple panels by Tim Patterson, student, College of the Redwoods, 1996.





Claro walnut box inlaid with spalted end-grain sycamore, bookmatched to form a bird image by Del Stubbs, 1982.


An active fungus colony surrounds itself with a chemical and physical barrier that defines its outer boundaries. Filaments of the fungus pack and swell in these regions and exude generous amounts of pigmented material that usually appear as black lines. The material in these “zone lines” protects the colony from attack by bacteria, insects, and other fungi, and assists in maintaining a desirably moist atmosphere. Inset: Electron microscope view of a fungus zone line in front of wood cell structures.



Worm-spalted red maple bowl by Alan Lacer, 1998. Typical spalting differs from worm spalt, where the worm hole allows the fungus to enter and work from the inside out.



Working Spalted Wood Safely

There is anecdotal and some medical evidence that substances from decaying wood are a health threat. Allergic reactions and some serious lung diseases have been traced to spores and fungi that inhabit rotting wood. The effect on an individual woodworker depends on his or her tolerance to the spores and fungi, the concentration of them in the environment and the length of exposure. Persons with weakened immune systems, lung illnesses or who show signs of allergic reactions to the spalted wood should avoid the material altogether. One must err on the side of caution when working spalted wood. Freshly sawn green material with active spores and fungi, or even air-dried material, is potentially the most hazardous. Kiln drying, by turning up the heat and driving out the moisture, will actually kill both fungi and spores. To avoid breathing spalted wood dust, I strongly recommend that you wear a respirator—not a nuisance mask—and have an effective point-of-origin dust collection system or a self-contained air filtration helmet. Avoid prolonged contact with your skin, and clean your work area thoroughly following any work with spalted wood.

 

Spalted Wood

Spalted Wood

By Alan Lacer


When wood is captured somewhere between the extremes of being completely sound and fully rotten, it can display magnificent beauty. The discoloration, prominent black lines and changes in texture that occur during the decaying process are known to woodworkers as spalting.

Spalting is a by-product of the rotting process that is carried out by a vast army of stain, mold and decay fungi. They are abundantly present in the air and soil, waiting for favorable conditions and a suitable host. Generally, wood moisture content of at least 25 percent, temperatures from about 40- to 90-degrees F, air and food (especially abundant in sap wood) are what the fungi need. A tree or branch freshly fallen onto a damp forest floor in warm weather is asking for it.

Lighter colored woods offer the best canvas for nature’s graphic work. Hard maple is viewed as the king of spalted woods, although sycamore, persimmon, red and white oak, elm, pecan, birch, buckeye, apple, magnolia, beech, holly, hackberry, box elder and the sapwoods of walnut and cocobolo are favored by woodworkers as well.


Where to find spalted wood

You can purchase spalted wood—usually maple—from specialty lumber and mail order suppliers (see Sources, below). Turning blocks are most easily found, but a few suppliers offer boards when they can get them.

Hunting spalted wood is like panning for gold—lots of searching for that one precious nugget. Logs rotting on the forest floor, dead limbs and entire dead standing trees are excellent sources. You can also hunt for hidden treasure at a community bone yard of removed trees, and don’t overlook the bottom of your old firewood pile.


Make your own spalted wood

Woodworkers commonly use these methods to cause wood to spalt. They will work most effectively if the temperature is kept where the fungi will thrive, between 60- and 80-degrees F. Monitor the spalting progress monthly—the optimal conditions you’ve created can make it happen fast.

• Place a freshly cut log section 2 to 3 ft. long upright on the bare ground. Put a shovel of dirt on the top end and cover it loosely with black plastic.

• Bury a log, freshly sawn green boards or green rough-turned bowls in damp sawdust containing pieces of rotten wood with active fungi. Keep the sawdust moist.

• Use plastic bags or plastic garbage cans to hold short sections of green wood or rough-turned bowls. Adding some soil or rotting sawdust may speed the process, although the fungi already present in the air or on the wood surface is probably enough to get it going. Leave the bags or cans with a small opening to allow for some air exchange.


How to stabilize spalted wood

Remove those things the fungi need to grow, and you’ll stop its progress. One method is to lower the wood’s moisture content.Wood below 25-percent moisture content, when kept in low relative humidity, is not likely to decay or even stain. Accomplish this by air or kiln drying, placing smaller pieces in a microwave or finish turning if the piece was a rough-turned bowl. You can also raise or lower the wood’s temperature. Spalting rarely occurs above 90-degrees F and stops below 32-degrees F. Some turners store blanks in a freezer prior to finish turning. Finally, you can restrict the air—no air, no decay. Logs submerged in water, for example, do not decompose from fungi. Tightly wrapping the wood in several layers of plastic will restrict the air and slow the growth of the fungi.

 

Working properties

If you’re lucky, you’ll catch the spalting at the right time, before the cellular structure of the wood deteriorates, and you’ll be able to work the piece without any trouble. Sometimes, however, the material will have areas that have become soft and punky. These areas have no strength and defy normal woodworking strategies. They will crumble, tear out in chunks or leave a wrinkled appearance when you try to cut or plane them. They refuse to be glued together, and leave you with a cratered, uneven surface when you try to sand. Though not suitable for joinery, these soft areas can often be stiffened enough to finish so the piece of wood can still be used decoratively.

You can saturate soft areas with a liquid hardener. Where the wood is only marginally soft, a spot coat or two of clear shellac or nitrocellulose sanding sealer may harden it sufficiently. A really punky spot will require cyanoacrylate (CA) glue (the thin, watery type) or a product made to stabilize rotten wood. There are a number of them sold as wood hardeners at hardware stores. It may take several generous applications to treat each bad spot. These hardeners are effective, but they have side effects. They fill the wood cells, so surfaces treated with them can’t be glued and oil finishes don’t take well because they can’t penetrate. Solvent-based hardeners and CA glues darken the wood considerably. I like Protective Coatings Petrifier (see Sources, below). It’s a water-based hardener that doesn’t discolor the wood, yet seals and stiffens effectively. It’s an excellent choice for troublesome soft spots.

You should be able to work the stiffened surface with edge tools—make very light cuts—or with abrasives, taking care to provide a firm, flat backing for the sandpaper. Some turners use body grinders or stiffbacked sanding discs and work the piece while it’s spinning on the lathe. For flat lumber, an abrasive planer is an excellent option, followed by a randomorbit or pad sander. If you sand by hand, use a sanding block to give firm support to the paper.

 

Finishing

You are likely to encounter three problems when you finish spalted wood: Splotching, yellowing and excessive darkening. The whiter woods—which usually have the most dramatic examples of spalting—can turn quite yellow with certain finishes, and because the soft areas act like end-grain or even a sponge, splotching or excessive darkening can result unless the piece is sealed first. An effective weapon against splotching is clear, dewaxed shellac used as a sealer. (Spray cans of shellac are thinned and dewaxed.) Cover the entire piece with a thin coat and let it dry. Then recoat dull-looking areas until all surfaces have a uniform sheen. You can use almost any finish as a topcoat over dewaxed shellac after it’s been sanded.

To minimize yellowing and darkening, use a surfacefilm finish like clear shellac or lacquer. Waterborne finishes dry clear and don’t yellow with age. If the piece is primarily decorative and has few, if any, soft areas, clear wax is appropriate.

If you don’t mind the yellowing and darkening, use your favorite oil finish, but be prepared to make many applications to the softer areas. Experience has taught me that an oil-finished spalted piece will appear rather muddy and uneven at first, but will look better as the finish cures, which can take weeks or even months. Some oil finishes (such as General Finishes Sealacell Step 1, see Sources, below) are essentially a thinned, light-colored varnish, and will not yellow as much.

If you are looking for a challenge, and effects that often surpass the wildest woods from the tropics, spalted wood may be your ticket. Each block of wood has its own unique properties that must be judged and worked on its own terms. Use spalted wood and your work will never go unnoticed. Use it well, and you’ll produce a real showstopper.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Flat material suppliers:

Northwest Timber
P.O. Box 1010
Jefferson, OR 97352
541-327-1000


Randel Woods
P.O. Box 96
Randel,WA 98377
360-497-2071


Talarico Hardwoods

RD #3 Box 3268
Mohnton, PA 19540-9339
610-775-0400

 

Bigleaf Maple:

Mount. Cheam Woodworking
8359 Banford Road
Chilliwack, B.C.V20GH3
604-795-9297

 

Turning stock suppliers:

One Good Turn
6064 S. 300 W. #11
Murray, UT 84107
801-266-1578


Choice Woods
833 W. Main St.
Louisville, KY 40202
888-895-7779


Craft Supplies USA

1287 E. 1120 S.
Provo, UT 84606
800-551-8876


Hot Stuff CA Glue
Satellite City, P.O. Box 836
Simi Valley, CA 93062
800-786-0062


P. C. Petrifier
Protective Coatings
221 S. 3rd St.
Allentown, PA 18102
800-220-2103


General Finishes
Sealacell Step 1
P.O. Box 51567
New Berlin,WI 53151
800-888-8286

 

For further reading:

"Sculpting Wood" by Mark
Lindquist, 1986, Worcester, Mass., Davis Publications, 800-533-2847. Mark and his father Mel have been pioneers in working spalted wood and in popularizing its use as a decorative material.

"Understanding Wood" by Bruce Hoadley, 1980, Newtown, Conn., Taunton Press, 800-888-8286.


This story originally appeared in American Woodworker December 1999, issue #77.

December 1999, issue #77

Purchase this back issue.

Click any image to view a larger version.


Cabinet on Stand English oak with spalted bigleaf maple panels by Tim Patterson, student, College of the Redwoods, 1996.





Claro walnut box inlaid with spalted end-grain sycamore, bookmatched to form a bird image by Del Stubbs, 1982.


An active fungus colony surrounds itself with a chemical and physical barrier that defines its outer boundaries. Filaments of the fungus pack and swell in these regions and exude generous amounts of pigmented material that usually appear as black lines. The material in these “zone lines” protects the colony from attack by bacteria, insects, and other fungi, and assists in maintaining a desirably moist atmosphere. Inset: Electron microscope view of a fungus zone line in front of wood cell structures.



Worm-spalted red maple bowl by Alan Lacer, 1998. Typical spalting differs from worm spalt, where the worm hole allows the fungus to enter and work from the inside out.



Working Spalted Wood Safely

There is anecdotal and some medical evidence that substances from decaying wood are a health threat. Allergic reactions and some serious lung diseases have been traced to spores and fungi that inhabit rotting wood. The effect on an individual woodworker depends on his or her tolerance to the spores and fungi, the concentration of them in the environment and the length of exposure. Persons with weakened immune systems, lung illnesses or who show signs of allergic reactions to the spalted wood should avoid the material altogether. One must err on the side of caution when working spalted wood. Freshly sawn green material with active spores and fungi, or even air-dried material, is potentially the most hazardous. Kiln drying, by turning up the heat and driving out the moisture, will actually kill both fungi and spores. To avoid breathing spalted wood dust, I strongly recommend that you wear a respirator—not a nuisance mask—and have an effective point-of-origin dust collection system or a self-contained air filtration helmet. Avoid prolonged contact with your skin, and clean your work area thoroughly following any work with spalted wood.

 

Spalted Wood

Spalted Wood

By Alan Lacer


When wood is captured somewhere between the extremes of being completely sound and fully rotten, it can display magnificent beauty. The discoloration, prominent black lines and changes in texture that occur during the decaying process are known to woodworkers as spalting.

Spalting is a by-product of the rotting process that is carried out by a vast army of stain, mold and decay fungi. They are abundantly present in the air and soil, waiting for favorable conditions and a suitable host. Generally, wood moisture content of at least 25 percent, temperatures from about 40- to 90-degrees F, air and food (especially abundant in sap wood) are what the fungi need. A tree or branch freshly fallen onto a damp forest floor in warm weather is asking for it.

Lighter colored woods offer the best canvas for nature’s graphic work. Hard maple is viewed as the king of spalted woods, although sycamore, persimmon, red and white oak, elm, pecan, birch, buckeye, apple, magnolia, beech, holly, hackberry, box elder and the sapwoods of walnut and cocobolo are favored by woodworkers as well.


Where to find spalted wood

You can purchase spalted wood—usually maple—from specialty lumber and mail order suppliers (see Sources, below). Turning blocks are most easily found, but a few suppliers offer boards when they can get them.

Hunting spalted wood is like panning for gold—lots of searching for that one precious nugget. Logs rotting on the forest floor, dead limbs and entire dead standing trees are excellent sources. You can also hunt for hidden treasure at a community bone yard of removed trees, and don’t overlook the bottom of your old firewood pile.


Make your own spalted wood

Woodworkers commonly use these methods to cause wood to spalt. They will work most effectively if the temperature is kept where the fungi will thrive, between 60- and 80-degrees F. Monitor the spalting progress monthly—the optimal conditions you’ve created can make it happen fast.

• Place a freshly cut log section 2 to 3 ft. long upright on the bare ground. Put a shovel of dirt on the top end and cover it loosely with black plastic.

• Bury a log, freshly sawn green boards or green rough-turned bowls in damp sawdust containing pieces of rotten wood with active fungi. Keep the sawdust moist.

• Use plastic bags or plastic garbage cans to hold short sections of green wood or rough-turned bowls. Adding some soil or rotting sawdust may speed the process, although the fungi already present in the air or on the wood surface is probably enough to get it going. Leave the bags or cans with a small opening to allow for some air exchange.


How to stabilize spalted wood

Remove those things the fungi need to grow, and you’ll stop its progress. One method is to lower the wood’s moisture content.Wood below 25-percent moisture content, when kept in low relative humidity, is not likely to decay or even stain. Accomplish this by air or kiln drying, placing smaller pieces in a microwave or finish turning if the piece was a rough-turned bowl. You can also raise or lower the wood’s temperature. Spalting rarely occurs above 90-degrees F and stops below 32-degrees F. Some turners store blanks in a freezer prior to finish turning. Finally, you can restrict the air—no air, no decay. Logs submerged in water, for example, do not decompose from fungi. Tightly wrapping the wood in several layers of plastic will restrict the air and slow the growth of the fungi.

 

Working properties

If you’re lucky, you’ll catch the spalting at the right time, before the cellular structure of the wood deteriorates, and you’ll be able to work the piece without any trouble. Sometimes, however, the material will have areas that have become soft and punky. These areas have no strength and defy normal woodworking strategies. They will crumble, tear out in chunks or leave a wrinkled appearance when you try to cut or plane them. They refuse to be glued together, and leave you with a cratered, uneven surface when you try to sand. Though not suitable for joinery, these soft areas can often be stiffened enough to finish so the piece of wood can still be used decoratively.

You can saturate soft areas with a liquid hardener. Where the wood is only marginally soft, a spot coat or two of clear shellac or nitrocellulose sanding sealer may harden it sufficiently. A really punky spot will require cyanoacrylate (CA) glue (the thin, watery type) or a product made to stabilize rotten wood. There are a number of them sold as wood hardeners at hardware stores. It may take several generous applications to treat each bad spot. These hardeners are effective, but they have side effects. They fill the wood cells, so surfaces treated with them can’t be glued and oil finishes don’t take well because they can’t penetrate. Solvent-based hardeners and CA glues darken the wood considerably. I like Protective Coatings Petrifier (see Sources, below). It’s a water-based hardener that doesn’t discolor the wood, yet seals and stiffens effectively. It’s an excellent choice for troublesome soft spots.

You should be able to work the stiffened surface with edge tools—make very light cuts—or with abrasives, taking care to provide a firm, flat backing for the sandpaper. Some turners use body grinders or stiffbacked sanding discs and work the piece while it’s spinning on the lathe. For flat lumber, an abrasive planer is an excellent option, followed by a randomorbit or pad sander. If you sand by hand, use a sanding block to give firm support to the paper.

 

Finishing

You are likely to encounter three problems when you finish spalted wood: Splotching, yellowing and excessive darkening. The whiter woods—which usually have the most dramatic examples of spalting—can turn quite yellow with certain finishes, and because the soft areas act like end-grain or even a sponge, splotching or excessive darkening can result unless the piece is sealed first. An effective weapon against splotching is clear, dewaxed shellac used as a sealer. (Spray cans of shellac are thinned and dewaxed.) Cover the entire piece with a thin coat and let it dry. Then recoat dull-looking areas until all surfaces have a uniform sheen. You can use almost any finish as a topcoat over dewaxed shellac after it’s been sanded.

To minimize yellowing and darkening, use a surfacefilm finish like clear shellac or lacquer. Waterborne finishes dry clear and don’t yellow with age. If the piece is primarily decorative and has few, if any, soft areas, clear wax is appropriate.

If you don’t mind the yellowing and darkening, use your favorite oil finish, but be prepared to make many applications to the softer areas. Experience has taught me that an oil-finished spalted piece will appear rather muddy and uneven at first, but will look better as the finish cures, which can take weeks or even months. Some oil finishes (such as General Finishes Sealacell Step 1, see Sources, below) are essentially a thinned, light-colored varnish, and will not yellow as much.

If you are looking for a challenge, and effects that often surpass the wildest woods from the tropics, spalted wood may be your ticket. Each block of wood has its own unique properties that must be judged and worked on its own terms. Use spalted wood and your work will never go unnoticed. Use it well, and you’ll produce a real showstopper.


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Flat material suppliers:

Northwest Timber
P.O. Box 1010
Jefferson, OR 97352
541-327-1000


Randel Woods
P.O. Box 96
Randel,WA 98377
360-497-2071


Talarico Hardwoods

RD #3 Box 3268
Mohnton, PA 19540-9339
610-775-0400

 

Bigleaf Maple:

Mount. Cheam Woodworking
8359 Banford Road
Chilliwack, B.C.V20GH3
604-795-9297

 

Turning stock suppliers:

One Good Turn
6064 S. 300 W. #11
Murray, UT 84107
801-266-1578


Choice Woods
833 W. Main St.
Louisville, KY 40202
888-895-7779


Craft Supplies USA

1287 E. 1120 S.
Provo, UT 84606
800-551-8876


Hot Stuff CA Glue
Satellite City, P.O. Box 836
Simi Valley, CA 93062
800-786-0062


P. C. Petrifier
Protective Coatings
221 S. 3rd St.
Allentown, PA 18102
800-220-2103


General Finishes
Sealacell Step 1
P.O. Box 51567
New Berlin,WI 53151
800-888-8286

 

For further reading:

"Sculpting Wood" by Mark
Lindquist, 1986, Worcester, Mass., Davis Publications, 800-533-2847. Mark and his father Mel have been pioneers in working spalted wood and in popularizing its use as a decorative material.

"Understanding Wood" by Bruce Hoadley, 1980, Newtown, Conn., Taunton Press, 800-888-8286.


This story originally appeared in American Woodworker December 1999, issue #77.

December 1999, issue #77

Purchase this back issue.

Click any image to view a larger version.


Cabinet on Stand English oak with spalted bigleaf maple panels by Tim Patterson, student, College of the Redwoods, 1996.





Claro walnut box inlaid with spalted end-grain sycamore, bookmatched to form a bird image by Del Stubbs, 1982.


An active fungus colony surrounds itself with a chemical and physical barrier that defines its outer boundaries. Filaments of the fungus pack and swell in these regions and exude generous amounts of pigmented material that usually appear as black lines. The material in these “zone lines” protects the colony from attack by bacteria, insects, and other fungi, and assists in maintaining a desirably moist atmosphere. Inset: Electron microscope view of a fungus zone line in front of wood cell structures.



Worm-spalted red maple bowl by Alan Lacer, 1998. Typical spalting differs from worm spalt, where the worm hole allows the fungus to enter and work from the inside out.



Working Spalted Wood Safely

There is anecdotal and some medical evidence that substances from decaying wood are a health threat. Allergic reactions and some serious lung diseases have been traced to spores and fungi that inhabit rotting wood. The effect on an individual woodworker depends on his or her tolerance to the spores and fungi, the concentration of them in the environment and the length of exposure. Persons with weakened immune systems, lung illnesses or who show signs of allergic reactions to the spalted wood should avoid the material altogether. One must err on the side of caution when working spalted wood. Freshly sawn green material with active spores and fungi, or even air-dried material, is potentially the most hazardous. Kiln drying, by turning up the heat and driving out the moisture, will actually kill both fungi and spores. To avoid breathing spalted wood dust, I strongly recommend that you wear a respirator—not a nuisance mask—and have an effective point-of-origin dust collection system or a self-contained air filtration helmet. Avoid prolonged contact with your skin, and clean your work area thoroughly following any work with spalted wood.