One of the most celebrated chemical combinations used to color wood is ferrous sulfate followed by potassium dichromate.
At the turn of the twentieth century, brothers Charles and Henry Greene were highly esteemed architects who had a prominent influence on the American Arts and Crafts movement. The scope of their work eventually evolved into designing the whole house: furniture and interior finishes as well as architecture. Perhaps their most well-known creations are the Gamble house and the Blacker house, both historical landmarks in Pasadena, California.
Brian has restored several Green & Greene homes, and worked with his team for two years refinishing the entire interior and exterior of the Blacker house after it was bought by Harvey and Ellen Knell in 1995. Although Brian came highly recommended to the Knells, they were understandably apprehensive about hiring someone they didn’t know for a job that was so critical to the home’s overall appearance.
“Don’t worry!” Brian reassured the couple. “I just finished a six-week correspondence class in finishing, so I know what I’m doing!” Fortunately for Brian, the Knells know a joke when they hear one.
However, it was back when he was restoring Charles Greene’s personal residence that he discovered the secret to the Greene’s signature coloration. He knew they often used ferrous sulfate to color their wood, but he knew there was more than ferrous sulfate on the Port Orford cedar that figured prominently as architectural millwork throughout the house. He scraped a small sample of the wood and sent it to a chemical-analysis facility. The report listed evidence of chromium as well as ferrous sulfate, and Brian had an “Aha” moment when he realized the second chemical influencing the wood’s color was potassium dichromate.
After much experimentation, Brian determined that the Greene’s applied ferrous sulfate first, and after that chemical dried, they applied potassium dichromate. This was a very popular method for coloring wood in Europe during the early part of the twentieth century.
You can vary the strengths of both solutions to achieve different colors, but here is a starting formula:
Recipe for Ferrous Sulfate + Potassium Dichromate
First apply the ferrous sulfate:
⅛ tsp of ferrous sulfate
4 oz. of hot distilled water
4 oz. cold distilled water
Slowly add one-eighth teaspoon of ferrous sulfate into four ounces of hot distilled water, stirring continuously. When the crystals have dissolved, add four ounces of cold distilled water and mix thoroughly. Strain the solution into a new container and wait for it to cool to room temperature before applying it to your wood. Wipe off the excess with a rag.
While you are waiting for the ferrous sulfate to dry on the wood, make the potassium dichromate solution. If you have applied tannic acid to the wood before applying the ferrous sulfate, you do not need to apply another solution of tannic acid before applying the potassium dichromate. When you are certain that the wood is completely dry, apply the potassium dichromate solution:
1 tsp of potassium dichromate
3 oz. of hot distilled water
3 oz. of cold distilled water
Slowly stir one teaspoon of potassium dichromate into three ounces of hot distilled water. Mix until thoroughly dissolved and then add three ounces of cold distilled water. Mix thoroughly. Strain this solution into a clean container and apply when it has come to room temperature. Wipe the surface of the wood with a rag before the solution dries. Do not sand until after you have applied your first coat of finish.
Alder
Cherry
Mahogany
Maple
Oak
Walnut
