Hi... all you CRCers! Hey, how often have you restored or cleaned up an old radio only to find that there was one piece you just couldn't bring back to life - the bezel or escutcheon. It's either corroded or it's finish is worn away from being rubbed for years by fingers twisting away at those adjacent tuning knobs. It's not common to find a radio that was manufactured with a colored enamel or lacquer coated bezel. These parts were normally chemically coated in order to obtain the distinctive "antique" look. So, I did some research and came across information on how to obtain a number of different chemical colorings for the metal stampings that comprise most radio bezels - and other parts too.
To begin with, there's one word that has to be constantly on your mind if your seriously thinking about doing this kind of refinishing work - SAFETY, SAFETY, SAFETY. Some of these chemicals are caustic and irritating. You MUST work in a well ventilated area, and with appropriate protective clothing and eye covering. Any containers that you use must be capable of being completely cleaned after use or are disposable. Finally, you need to work in an area were spills, fumes and/or other contaminations will not be a problem.
A word (actually 4 words) about chemical supplies. You're on your own. Most good size cities have chemical supply houses. Some materials can be obtained through photographic and large hobby supply stores. However, part is parts. That is, most other items that you'll need will be found in your own shop or the local hardware store.
The first step in coloring a metal piece is that the piece be made free of it's old finish and be scrupulously clean. One of the biggest problems for bezels is that they're stamped designs have hard to reach inside edges and creases. So, simple steel wooling or rubbing with pumice might not get the piece entirely striped and clean. You can try a soft buffing wheel and/or a warm bath of TSP cleaning solution scrubbed on with a tooth brush. If you'll remember, Dave Boyle gets good results by soaking parts in dish washer soap overnight. My source material says that any existing or remaining oxide finish can be removed with a pickle bath. Their common pickling bath is 10 parts water to one part sulphuric acid. Remember your high-school chem lab, always pour the acid slowly into the water, NOT the other way!
It's also important to look closely at the finish of the cleaned part. If you want a matte finish on the colored surface then the piece itself must have a matte finish. If there was some corrosion, which caused a crusty looking spot, then this spot will show up in the finish as well if it's not taken off.
A little farther down this article I make mention of "scratch brushing". This is nothing more than rubbing the finish with fine '0000' steel wool, a brass brush or greasless polishing compound to give the piece an antique look. The idea is to remove some of the finish, sometimes with a brushed look, so that the upper surfaces of the stamping appear to have highlights. Usually this is technique is done while the piece is wet. One reference talked about a metalsmith that used beer(!). Did I miss the point?
In any case, the surface of the cleaned and ready piece should not be touched and it should be colored immediately after being prepared to avoid further oxidation. You may also want to consider techniques like spraying the final surface with a matte or semi-gloss lacquer or apply a paste waxing to seal and create the desired patina on your finished work.
Okay, onto the coloring techniques. The one thing that the sources harp on is that because of variables like temperature, concentrations of solutions, alloy types, timing and other factors, results will likely vary. This means that you'll probably want to do some experimenting, on a test piece, in order to determine your technique for the desired results. One other note; the following formulas are for brass and copper. If you have a bezel or some other part made of another metal alloy, then you'll probably have to have it lightly plated with brass or copper to get the desired results.
The following formula is for copper only;