Sounding like a mystery ingredient in a junk food snack, potassium dichromate has been used for hundreds of years to color wood furniture. In particular, it is frequently associated with its use on French Empire furniture during the early 1800s when Napoleon was determined to bring a magisterial grandeur to French architecture and decorative arts. Consequently the costliest woods—particularly Cuban mahogany—were treated with potassium dichromate to enhance the wood’s lustrous colors.
On a lighter note, potassium dichromate is also a frequent ingredient in fireworks—not for its color but for its ability to lower the ignition temperature of other chemicals in the mix. This does not mean that potassium dichromate is explosive.
Also known as bichromate of potash, the chemical is often referred to by those within the wood finishing profession by its nicknames of “PD” or simply “dichromate. “It is readily available through chemical supply houses and it arrives in the form of bright orange/red crystals. It is very carcinogenic so be sure to wear gloves, eye protection and a mask while working with it. If you store potassium dichromate in a non-reactive container and keep it in a cool dark place, it has an almost infinite shelf life.
Despite its carcinogenic nature, potassium dichromate still remains one of the most popular chemicals for coloring walnut and mahogany. It typically deepens and enriches the inherent warm tones on these two woods as it reacts to the tannic acid within them. On maple however, which is void of tannic acid, it merely deposits its own color, leading to a rather weathered look. The effect is similar to the gray tones of ferrous sulfate, but with more pronounced background tones of yellow. Applying a wash of tannic acid to maple before applying the dichromate significantly changes the color effect to a mellowed brown color with blond undertones. This was shown on page 22.
Recipe for Potassium Dichromate
½ tsp of potassium dichromate
4 oz. hot distilled water
4 oz. cold distilled water
Slowly add ½ teaspoon of potassium dichromate to four ounces of hot distilled water while stirring continuously. When the crystals are dissolved, add four ounces of cold distilled water to the solution. Stir until the solution is thoroughly mixed, then strain through a cone into a clean container and apply the solution when it has come to room temperature. Wipe the surface with a rag before the solution dries.
Are you old enough to remember when the powdered drink Tang first came out and it was considered space-age? Well, potassium dichromate may look like Tang when you see it inside a container, but trust me, you definitely don’t want to drink this stuff! Or even touch it without wearing gloves!
Alder
Cherry
Mahogany
Maple
Oak
Walnut
