Potassium dichromate: chemically coloring wood

The question comes up occasionally about using chemicals to change the color of wood. Usually the desired result is the color of aged wood--cherry and mahogany come immediately to mind as woods that develop rich, lustrous color when they are aged. Aging is free, but it's slow, and we're impatient woodworkers here in the 21st century.

Dye stains can darken cherry or mahogany quickly, but the wood beneath the dye does continue to darken with age, and you can wind up with a darker piece than you really intended.

So, is it possible to "hurry up" aging wood with chemicals? For some woods, yes. According to Understanding Wood Finishing, by Bob Flexner, Potassium dichromate reacts with tannic acid in wood. So woods with tannic content--oak, cherry, walnut, and mahogany--are good candidates for using dichromate coloring.

Dichromate is available from a variety of sources, and the price can vary widely. I obtained a pound on ebay for under twenty dollars. As you'll see shortly, this is a lifetime supply. Dichromate is an orange powder. It dissolves in warm water to make a vivid orange solution.

Dichromate is a hazardous chemical. Handle it with caution as you would with any wood finishing chemical. The powder is especially damaging to mucous membranes, so wear googles and a mask when you mix, and add the powder to the water instead of the other way around.

David Marks has an article up suggesting 1 teaspoon of dichromate mixed with 1 cup of water as a starting point. For you metric users, that works out to about 9 grams in 250 mL of water.

I mixed up a batch by these instructions, and used a foam brush to paint it onto samples of walnut, cherry, mahogany and oak. I'll let the pictures do the talking.

The effect on mahogany is astonishing. Within a half hour the wood takes on a deep, rich coloration. All the luster of the grain and figure remains--the light plays off the grain the same as before the coloration. The look is not muddy or blotchy.

Cherry can be a difficult wood to stain. but it takes the dichromate treatment well. I might mix a more dilute solution than the Marks formula above--cherry responds profoundly to the chemical.

Walnut is suprising. the dichromate depens the color without obscuring the grain at all. It's more of what you buy walnut for.

And on oak the effect is more subtle. It didn't knock me out at first but I really got to like it after a while..

Since this is a water solution, you'll probably want to take the time to wet your piece with water before coloring, then dewhisker your work after it dries. The water will raise some grain, and you'll want to avoid having that telegraph through your finish. By doing that first, you avoid having to sand the colored wood.

I'll put some more pics up in this tutorial once I get some time to take the test pieces through a final finish. I have read a lot of conflicting information about this technique (even Flexner discourages you from trying it!), so I had to try it myself. I highly recommend this method of aging for cherry, walnut, and most especially mahogany.

I put a few coats of wipe-on poly on the samples, so show a more realistic contrast:

Give this a try. It's well worth the effort to find a source.