18
Logwood
For an immediate visual understanding of the effects of mordants on natural dyes, look at the difference in the wood samples here. After applying a solution of logwood extract to all the samples, potassium dichromate was applied to one set as a mordant and ferrous sulfate was applied to the other set. The dichromate produced a distinctive reddish coloration on walnut, oak, cherry and mahogany and a pinkish cast reminiscent of aromatic cedar on alder and maple, both of which do not contain tannic acid. Ferrous sulfate, on the other hand, turned all the samples a rich complex black color.
Now in reverse, to see the effects of dyes on wood, look at the samples that have only been treated with ferrous sulfate (Chapter 8, pages 34–36) or only treated with potassium dichromate (Chapter 12, pages 53–55) without being dyed with logwood first. You will notice that the dichromate by itself deepens the existing color of the wood (with no additional reddish cast) and the ferrous sulfate by itself adds a gray tone to the wood.
Logwood is also known as campeche or bloodwood, and it is derived from the heartwood of the logwood tree, which is found in central America—primarily Guatemala, Belize and Mexico where it was used in herbal medicine. Like brazilwood and cochineal, logwood was exploited by European traders as a quite profitable export until the advent of synthetic dyes. The old adage of “You can’t judge a book by its cover” is especially applicable to logwood because it looks red, akin to Hungarian paprika powder, in the container, then appears yellow on the wood until you add the mordant.
When combined with ferrous sulfate, logwood is used to achieve an effect on wood called ebonizing. This is a centuries-old technique that is currently in vogue again. True black ebony comes from the heartwood of Gaboon ebony, which has very little to no visible grain pattern but is known instead for its extraordinary luster after polishing. Due to over harvesting, Gaboon ebony is now a critically endangered species, and it is illegal to import it into the United States. The technique of ebonizing wood with a logwood/ferrous sulfate solution offers that same jet-black color but still allows you to see a faint grain pattern of the species to which the solution has been applied. Some finishers think this background hint of grain pattern gives ebonized wood greater depth and interest than real ebony.
This is a substantially different effect than you would get from painting the wood black or dying it with India ink because those substances mask the grain characteristics, resulting in a flattened black effect. Similarly, logwood’s advantage in ebonizing wood compared to using a synthetic black dye is that logwood produces a more mature, complex, black because of its subtle hints of reddish brown undertones.
It is better to use logwood extract, as opposed to logwood chips. The extract is more expensive but it is also more concentrated. It is readily available online and has an indefinite shelf life.
Recipe for Logwood Extract + Ferrous Sulfate (Ebonizing)
You want to apply both solutions hot for better penetration, which will heighten the reaction on the wood.
Logwood Extract:
1 tsp of logwood extract
6 oz. of hot distilled water
Slowly stir one teaspoon of logwood extract into six ounces of hot distilled water and mix thoroughly. Strain the solution into a clean container and then apply it to the wood while hot. Wipe off the excess solution with a rag. When the wood is completely dry, apply the ferrous sulfate.
Alder
Cherry
Ferrous Sulfate:
1 tsp of ferrous sulfate
6 oz. of hot distilled water
Slowly stir one teaspoon of ferrous sulfate into hot distilled water and mix thoroughly. Strain into a clean container and apply to the wood while still hot. Wipe the surface with a rag before the solution dries. Do not sand until after you have applied your first coat of finish.
Mahogany
Maple
Oak
Walnut
Applying the solutions while hot makes them more effective because they penetrate deeper. However, it is important to keep the solution at the same hot temperature throughout the process to ensure an even color.
Recipe for Logwood Extract + Potassium Dichromate
Logwood Extract:
2 tsp of logwood extract
6 oz. of hot distilled water
Slowly stir two teaspoons of logwood extract into hot distilled water and mix thoroughly. Strain into a clean container and then apply to the wood. Wipe the solution off with a rag.
Potassium Dichromate:
½ tsp of potassium dichromate
4 oz. of hot distilled water
4 oz. of 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.
Alder
Cherry
Mahogany
Maple
Oak
Walnut