Dark etching DIY

An ancient iron finishing process, widespread for treating embellishment objects, artefacts subject to wear and knife and tool blades, not only to improve their aesthetics but also to protect them over time.

Burnishing or "bronzing" is a chemical oxidation process in which iron or steel (not stainless steel), reacting with an acidic chemical product, transforms the lattice of its surface, making it "brown". The blackish color is due to the type of iron oxide that is created on the surface, this oxide also gives greater protection against corrosion over time. To obtain a burnished blade (or any ferrous artefact) it is sufficient to immerse it in a special acid solution, usually based on ferric chloride; the concentration is not important but only determines the reaction speed.

The color nuance changes based on the mixtures used for the treatment, in fact other products or additives and/or catalysts specific to the desired effect can be used together with or instead of ferric chloride. The ferric chloride reported here, having low harmfulness compared to other products, is recommended for DIY operations and is also easily available. Artisanal burnishing is a true art, let's mention for example the splendid damask blades to which burnishing gives an elegant and refined veined effect.

To try your hand at burnishing old knives, you must first degrease them thoroughly, without touching them with your fingers and without leaving streaks; only then can the object be immersed in the darkening solution. Wait a few minutes until the degree of coloring you want to achieve; when finished, remove the blade and rinse it thoroughly with an alkaline solution, bicarbonate of soda is also fine. Pat dry, checking that the surface no longer releases any blackish colour. If desired, you can repeat the process to correct errors or increase coloration. As a final treatment we recommend passing the blade with an oil to increase its shine and preserve it over time.

For culinary use, be careful with kitchen knives because if you are not very familiar with carrying out this ad hoc technique, you could continue to smell the treatment and affect the food; obviously mineral oils or other harmful chemical products cannot be used for the final polishing, rather a light film of vegetable oil or animal fat can be used.