Columbia cel kills black paint

[Gasmask Ted]

The cel attached has lost almost all of its black paint (but not ink). I thought at first it was just where it wasn't shellaced tot he background, but that was on error. The black at the bottom is over a shellaced area. And I mean "over"; it's on the face of the cel, not the back. I confirmed the black pupils on some of my other Columbia cels are also a matte black on the face of the cels. It's a very clear line differentiating the remaining black tho. Anyone else seen blak paint lost in this way and know how it happened? My guess is the existing black was protected by a frame or matte now removed, but I'm surprised there would have been such a strong loss, and I'm not sure if it would just be due to plain weathering. If the rest of the black dissolves in a few years, I guess I'll have my answer.

Also, can anyone ID the short? I'm fairly sure it's not a '39; it would have to be two secondary characters I didn't catch in screens if it is. There a few Color Rhapsodies with Dog in the title and at least one with Bluebird.