Shellac Shellac Shellac is a resin secreted by a tropical beetle-like bug that was widely used as a binding agent in records during the heyday of 78rpm discs. The rest was inorganic filler. The shellac in discs is not like the liquid shellac varnish that you brush onto wood.
Moisture is a major problem to shellac disks.
Moisture tends to encourage the growth of mold and the breaking down of the shellac portion of the disks. You can see it and, of course, hear it.