Expert Answers: The solution for ebonizing consistency

By Rob Thompson March 8, 2024

The solution for ebonizing consistency

Preparing a solution for ebonizing wood from steel wool and vinegar seems like a magical and unpredictable process. Is there a way to get consistent results?

—Morgan Davies
Metairie, LA

Controlled magic. Steel wool reacts with white vinegar, in precise proportions, to result in a consistent ebonizing solution.

Combining steel wool and vinegar creates an iron acetate solution. This solution is what reacts with tannins in some wood species to create an ebonizing effect. A foolproof and optimal recipe for iron acetate ebonizing solution, like that for a tasty dessert, involves the best ingredients mixed in exact proportions and reacted under prescribed conditions, as informed by chemical principles.

Ingredients. Steel wool (iron, Fe) found in hardware stores comes in various grades. The finest grade (#0000), with the finest wire and largest surface area per gram, reacts the fastest. Briwax brand is especially fine, made from a 5-µm-thick ribbon. There’s no need to wash your steel wool or cut it into pieces.

Vinegar (acetic acid, CH₃COOH) is required by U.S. law to be produced by fermentation of alcohol, with phosphate as an added bacterial nutrient. Interestingly and coincidentally, phosphate is needed to catalyze our desired reaction. Thus, vinegar made by diluting pure acetic acid does not perform well, nor does apple cider vinegar that has suspended solids that can coat the steel wool. Use distilled white vinegar containing 5% acetic acid, the kind you can pick up at the grocery store.

Proportions. The chemical reaction is Fe + 2CH₃COOH → Fe(CH₃COO)₂ + H₂ (hydrogen gas). Using the right proportions of ingredients is critical to achieving good, consistent results. Too little vinegar in relation to steel wool causes solid iron acetate to form and, in some extreme cases, causes unwanted products of various colors. Too much vinegar dilutes the iron solution unnecessarily, leading to poorer ebonizing. The optimal amount of vinegar is 340 mL (1.5 cups) per 4.0 g of steel wool (about 1.5 inches of a Briwax roll).

Conditions. Run the reaction at room temperature in a non-metallic, uncovered, large-mouthed vessel to allow solution contact with air, since oxygen assists the reaction. After three days, filter out the remaining solids, resulting in a nearly clear, light green-brown solution. The solution quickly becomes red-colored in air as the ferrous acetate transforms into basic iron acetate Fe(II)Fe(III)₂O(C₂H₃O₂)₇(H₂O)₃.

Application. Apply the iron acetate solution sparingly to minimize any final cleanup. For example, just ¼ cup of ebonizing solution per 7 sq. ft. of surface is sufficient to darken oak.

A recipe backed by science

340mL (1.5 cups) distilled white vinegar, 5% acidity

4.0g #0000 steel wool

Combine ingredients in a non-metallic, uncovered, large-mouthed vessel. After 72 hours, filter the solution through a paper coffee filter. Wait for the green-brown solution to turn red before application.