Iron powder soaked in vinegar makes an interesting dye that can be black, gray, or brownish-red, depending on the application and use. Many craft makers and wood workers use this dye in creating an ebony finish on maple or pinewood. Iron dye is an old traditional finish (often used by colonial gunsmiths).
The Iron Dye is initially a mixture of iron acetate and iron oxides; however, it will later decompose and what remains on the wood is a just variety of iron oxides. Due to the fact that iron oxides are inorganic materials; the final stain will have a high resistance to UV light (sunlight) and may also be used for outdoor applications. Iron dye does not fade as many organic dyes do.
Iron dye is a good replacement to pigmented stains due to the fact that it will not just stay at the surface. When applied on a clean dry wood, the iron acetate solution goes deep into the wood and some oxides will form under the surface. For optimum protection in difficult weather conditions, Iron dye finishes are also covered with multiple coats of lacquer.
Materials you need:
- strong pickling vinegar (7% acetic acid)
- Iron powder (recommended grades are S100, S70, IRON100)
- Plastic buckets for making and storage.
How to make the Iron dye?
In a plastic bucket or glass jar add one cup of iron powder and 5 cups of vinegar. Loosely cover the container and leave it in a warm place. Swirl the container 3 or 4 times a day and about one minute each time. The iron dye will be ready after 2 days. Transfer the liquid to another container for use. Some iron powder will remain at the bottom of the container for future productions.
Warning: Do this outside or in a well ventilated place to avoid breathing hydrogen gas and vinegar.
How to apply the stain?
Depending on the final finish you expect, you may use one to 7 coats of the stain. The iron reacts with tannins to create the grey s and black.
Woods such as oak will have more tannins and will blacken when treated with the iron solution. Otherwise tannins must be added to the wood to get a black reaction. Black tea is a good source of tannin. A first coat of strong black tea can help you create a deeper and darker color.
The old time gunsmiths would heat-treat their maple stocks after treating them with the iron dye solutions. This method creates a sudden color change that is dramatic and interesting. It is especially effective for figured maple.
Comments by others
“I applied 7 coats of the mixture to a large ornate maple appliqué. Three coats of flat lacquer and the result was a deep rich brown that is just not yet black, with hues of reddish brown peeking through. Just gorgeous. I was trying to achieve an ebony finish, but what I got was better and magnificent.”
I have seen the maple finish done on a gunstock. The gunsmith I watched used a blowtorch to activate the color after wiping the iron vinegar solution onto the maple gunstock. He got a rich orange hue which appeared as the solution dried under the heat of the blowtorch. Since this technique dates from the colonial flintlock smiths (who favored maple), I am guessing that they would use whale oil lamps or candles/torches because I don’t think that they had blowtorches at that time.
Iron Dye Chemistry
When iron powder reacts with acetic acid, the derivative is a salt known as Iron II acetate, AKA ferrous acetate with formula (CH3COO2) Fe. It is a light brown or off-white solid ionic compound of iron. It is highly soluble in water and is used as both a mordant and a dye.
Another iron dye is Iron II sulfate. Iron sulfate may be made by chemical reaction of iron powder and diluted sulfuric acid; however, due to the corrosive nature of sulfuric acid and harmful hydrogen gas produced during this reaction, it might be best to buy ready made ferrous sulfate for your experiments. Ferrous sulfate, formula (FeSO4) is a blue green crystal commonly called green vitriol, copperas, or sulfate of iron. It turns to white when dried. Ferrous sulfate is used in making iron gall ink, grey wood and wool dye, dark grey when used with tannin, lawn conditioner, iron supplement, and other.
Ferrous sulfate produces grey on woods and will not produce reds or browns on wood, whereas ferrous acetate will. You are better off buying small amounts of either and making weighed formulas of each for use as dyes or mordents, as the affect of each is quite different depending on the formula strength.