Blackening Brass

This article describes a process from Jack Hudock for blackening brass parts.

Clean the parts first with files or emery paper, remove all oxidation, flux, or excess solder from the parts.

Pickle the parts using undiluted Muriatic Acid which is 30% Hydrochloric Acid (See figure 1) to remove any organic contaminates on the surface. White vinegar can also be used, it takes longer to work, but is safer.

Figure 1: Muriatic Acid

Muriatic Acid will eventually dissolve the brass so the length of time you leave the part in the acid depends on the thickness of the part. The time could be as short as a few 10s of seconds for thin photoetched parts to 15 minutes for parts that are 1/32” or more thick.

Rince the parts thoroughly with hot water, and don’t touch with bare fingers thereafter.

Dilute the blackening solution (see figure 2) 10 to 1, or even more, with distilled water. This slows the blackening process and makes it more controllable. Straight from the bottle, the black builds up too fast and too thick so it flakes off easily.

Figure 2: Blacking solutions

Soak the parts in the blackening solution agitating them from time to time, checking every 30 seconds for progress. Don’t aim for a 100% jet black. Remove the part and rinse thoroughly with hot water.

Buff with a soft cloth. Some black will probably come off. A second, shorter, run through the solution should do the trick.

Solder joints may need to be touched up with paint.

Parts list

Blackening chemicals

Both are available in multiple sizes and from multiple sources. The links are to the manufacture’s own web sites.

“Brass Black” by Birchwood Casey

“JAX Black” by JAX Chemicals

Muriatic Acid (hydrochloric acid) available at most hardware stores

2024-10-02