Intarsia is a three-dimensional mosaic or sculpture in wood. The process involves cutting, carving, and shaping individual pieces of a pattern, then gluing them together. Using different species of woods and varying their thickness, color, and grain can produce dramatic effects with depth and perspective.
There are no limits to the subject matter for intarsia: I've seen wonderful examples of wildlife, landscapes, religious icons, and corporate logos. If you think of intarsia as a marriage of art and woodworking, you'll realize, like any other art form, there are no set rules to follow. A successful intarsia piece pleases the eye, balances form and composition, and satisfies its creator.
Tools, Patterns and Wood Selection
You'll need a good variable speed scroll saw, a sharp knife, some files and chisels, and a selection of sandpapers to get started on your first project. Drum sanders (I like the inflatable, malleable kind), in combination with a flap wheel, are real time savers, and a rotary carver/sander works great for cleanup.
While the supptly of commercially available patterns is unlimited, your own ideas, pictures, and photographs can also be a wonderful source. Start with a simple pattern - something with 10 or 12 pieces - and get a feel for the technique. You'll quickly realize the key to success is interpreting your pattern: choosing the right species, colors, and grain patterns and even tweaking dimensions as necessary.
When selecting wood for your project, the first rule is to use dry wood, not green. After that, you must set aside the natural instinct to choose clear straight grain: knots, color variations, and other faults are to be prized because the wild grain patterns around these defects lend the finished piece dramatic highlights. While cedar is popular among intarsists, the finished results tend to blend together so stains become necessary. I prefer working in hardwoods, where the finished colors are more predictable. For example, white tiger maple makes great fur on a dog or wolf; a combination of walnut and white maple brings glory to a bald eagle's crown; and green poplar jumps to life as leaves or grass. I've had success making goose feathers out of chestnut and recently made a cowboy's hat out of butternut because it looks a lot like worn felt.
Transferring a Pattern
Based on early experiences, I strongly recommend not using graphite paper to lay out patterns. Instead, make several photocopies of the pattern, with all the parts numbered. Lay one copy on a flat surface and cover it with wax paper: this is your assembly area.
Cut out each piece of the pattern from a second photocopy and use spray adhesive to secure these cutouts to the various pieces of raw wood you have selected. This is probably the most important step, because it will lock you into specific grain and color patterns. Try cutting one individual piece out of an extra photocopy, then lay the sheet on the wood and move it around until the grain you like best appears in the hole you just cut.
To ensure a good fit later, cut each piece just outside the pattern line. Don't try to fix mistakes as you go, and don't take any shortcuts. For example, imagine you're cutting myriad feathers for an eagle's wing. It's tempting to cut ten or fifteen feathers from a single block, then fit them to the pattern. But the accumulated errors may be fatal: it's much safer to cut them one at a time and fit them as you go. While blade speed and size are factors, the critical element in successful cutting is feed rate. Go slow - pushing too fast flexes the blade and results in cuts that aren't square.
Shaping and Detailing
This is the fun part of the process, as each of the pieces falls into place. While sanding is a little messy, it's the most efficient way to achieve the final shape and detail. The edge of a disk sander and the contoured face of an inflatable drum work well for initial shaping - refinements are handled with rotary tools equipped with sanding and carving heads.
All the edges in intarsia must be contoured to some extent. Keep in mind the varying thicknesses of the wood will help here, but the larger pieces may need extra contouring. After a piece is cut, make sure the abrasive hits the top edge first and sticks to the pattern. Unless a piece is held absolutely vertical an angle will occur, ruining your piece.
I like to use a 90-minute epoxy to glue the parts together on the wax paper. I generally need that time to calmly line everything up. Spot glue at various points - the goal is to hold everything together until the entire assembly is glued permanently to its backer board. When the epoxy has set, lift the assembly and trace its outline on its ultimate backer before gluing it in place.
Assuming you have selected dramatically colored hardwoods and have patiently sanded each piece to 220 grit, the safest way to achieve a good finish on this multi-layered piece is to give it a good soaking in natural Danish oil. I like to apply two coats of oil (wiping them off according to the manufacturer's instructions), followed by a top coat of clear gel varnish once the oil has cured. If you're uncomfortable using the gel, buff with rouge, diamond grit, and carnauba wax in that order: you'll still get a beautiful, maintenance-free finish.