Remove Red Spots with Wright's Copper Cream
On an unlacquered horn, red spots are a red flag that something is wrong. Brass is only red when zinc is leaching out of the metal, leaving behind the red copper. This problem is called “dezincification”, or “red rot”, and the structure of the copper when the zinc is gone is like a brittle sponge with big gaps in the crystal structure. If enough zinc disappears, the resulting red spot becomes very fragile and will turn into a hole.
There are other kinds of red spots that can appear on the outside of the horn, and not all of them have the same implication as spots of red rot. The best way to tell is to attempt to clean them with Wright’s Copper Cream. It’s cheap and can be found at most grocery stores. Wright’s is a cream that is made with mostly citric acid and diatomaceous earth (a fine abrasive made from crushed up tiny fossils.) The slight abrasive gives a good scrubbing action and can clean off spots that would not be removed with a chemical polish such as Maas or Flitz.
A Word of Warning.
There are a few things to be careful of when using Wright’s Copper Cream. Most importantly, it must be rinsed away completely. When it dries, it leaves behind a powder that can cause all sorts of headaches if it finds its way into the valves. It also contains a small amount of ammonium which can cause stress fractures in untempered brass if it’s allowed to sit on the surface for a long period. (If you have a stress relieved horn from yours truly, it’s not an issue of course…) I often use my ultrasonic tank to remove the Wright’s but when that is not available, warm soapy water will do. Another thing to consider is that the very fine scrubbing action will scratch finely finished horns. I usually wait for a few years before using Wright’s on Medlin horns, preferring to stick to chemical polishes to preserve my jeweler’s finish. For horns that are a bit older, or not finished as well, Wright’s will do an excellent job of removing red spots and brightening the finish.
It's okay if after scrubbing there is a very slight pink tinge, but no more than slight.
If the spots do in fact come out with Wright’s than you are good to go. If they persist no matter how much you scrub, then there is a good chance that the core of the red rot goes deeper than just the surface. In that case, you have a spot of red rot and will need an experienced technician to advise you of your best option. In most cases, the spot will eventually need to be patched. Wright’s can also be used to clean the horn’s surface in a more general manner, not just for spot cleaning. Just remember to be careful and you can keep your horn looking swell!
Released in January 2018 newsletter