Dezincification or "Red Rot"
Not all dents can be made to disappear. The metal has stretched and the lacquer has stretched along with it. What you'll find is that even after the metal has been folded, stretched, or hammered back into place, there will be a foggy spot where the dent occurred. That is because the lacquer stretched on a microscopic scale. For Silver plated instruments this can be even more pronounced because of how easy it is to scratch silver. I ask customers to imagine metal like human skin, skin can only stretch so much before it tears and even if its sewn together a scar will remain.
Soldering is another repair that is usually pretty obvious when it is needed. Something is moving in an area that is supposed to be stiff, or there is a rattling sound, or maybe you can't even play the instrument because the leadpipe came off. Soldering itself is basically using a flame to bring two or more pieces of metal up to a certain temperature in order to melt Solder, imagine metal glue, and then cooled. If done properly the two or more pieces will hold. Depending on the needed strength of the soldered joint, greater and greater temperatures are required in order to melt the solder. This becomes a balance between heat needed to melt the solder and not applying too much heat and burning the lacquer of an instrument. Modern lacquers are tougher and able to take more heat while older lacquers typically cannot. No matter what steps are taken in order to protect the finish of an instrument, extreme heat is still being used. Its up to the technician to know which strength of solder is needed and how much heat need be applied.
Dezincification is a form of corrosion and weakening of brass instruments in which zinc is dissolved from the brass alloy. What causes this to occur? Spit sitting inside of the instrument. Human spit is acid in order to help breakdown food in our mouths. Everyone's biology is a little different so some people have more acidic spit than others. The process is internal, its very easy to not even know that dezincification has occurred. The acid essentially "eats" its way through the brass and eventually becomes visible with its tell tale pink or red coloring, thus the term "Red Rot." Its easier to see the damage on yellow brass instruments compared to silver because of the stark contrast in color.
Cleanings are among the most important maintenance requirements an instrument has. An instrument will not function properly if it is not cleaned on a regular basis more importantly costly repairs may accumulate. Cleaning is often the first step for brass instruments for most repairs. Is the first valve of my trumpet sticking because of a dent? Is the casing out of round? That may well be the case but unless the instrument is clean you can't eliminate old oil, spit, calcification, as the true underlying cause. My hand slide for my trombone won't go past 2nd position. Is there a dent? Are the slides misaligned? You won't know for sure unless the instrument is clean and this is why cleanings are so important.
Brasswind repairs can be boiled down to three main types, Dent Removal, Solder Work, and Professional Cleanings. In order for brass instruments to function properly, cleaning is usually the first step.
Silver plated brass instruments are just that, silver plated. Underneath the silver is brass. As the "Red Rot" progresses, flakes of silver can be seen coming off of the instrument. All brass instruments are susceptible to dezincification and the potential for structural failure. As "Red Rot" progresses the metal will become weaker and weaker until little pin sized holes appear and then the instrument has air leaking which can affect playability. Certain notes won't play correctly or even at all because you can't get enough airflow to reach higher notes. After the damage has occurred there are two ways of fixing the issue, soldering a patch over the hole or holes, or replacing the affected part. How can you prevent this from happening? Yearly cleanings. I ask customers to imagine myself as their dentist. Cleaning kits are your instruments "tooth brush" and players need to brush their teeth on a regular basis. Once or twice a year, depending how often you play, you bring the instrument in for its deep cleaning.
Dent Removal is pretty straight forward and is usually the easiest to notice. The bell of a trombone was round and now its flat; pretty easy. Some dents are much much more subtle like the casing of a trumpet being out of round. The valve, or piston, is round and is being pressed into a hole that is no longer round. Simple to understand but harder to see. The process of removal is typically done with steel mandrels and hammers that force the metal back into place.
The instrument is fully disassembled, degreased, ultrasonically cleaned, hand washed, reassembled, and hand polished.