Update: I had the good fortune to run into a metalurgist today and asked him about A chemical process that is analogous to polymerization but does not require heat. He said the process is anodizing. He told me that it would not involve a health risk for playing the melodica. It might change the sound from the reeds and the intonation, he agreed. He has some familiarity with free reed instruments. It looks like the product I have ordered, Hi-Gear SMT2514s SMT2 Synthetic Metal Treatment, will produce this effect. We’ll see. I’ll report on the results.