The material I use is Grafix' Dura-Lar (http://www.grafixplastics.com/mylar_duralar.asp), not the one that holmburgers' refers to. It's not biodegradable, AFAIK, and claims to be non-yellowing, which would suggest that it is relatively stable. It's definitely a polyester film, according to the MSDS, not CDA or CTA. But the (non-hardened) gelatin can be peeled off the surface relatively easily. I don't have any formalin or other hardening agents to test whether a hardened layer would do the same. There's also "Dura-Lar Wet Media" film, which has some sort of surface treatment, which I think is the other thing Chris refers to, but I don't know anything more about it than that.
Originally Posted by holmburgers
Hope that helps to clear things up...