On Tuesday, October 25, 2016 at 4:11:42 PM UTC-4, Jeff Liebermann wrote:
On Tue, 25 Oct 2016 12:00:08 +0100, N_Cook wrote:

Do you happen to know what causes contangion in rubber ?
If one band fails by stretching or going gooey, then the others usually
are failing in the same way. I'm assuming they are not of the same batch
at manufacturing and then the same ageing failure but some gas or
biological vector moving about inside a casing


Three things, from the most to least common, and depending on the composition of the material:

a) Ozone - Ozone will attack both synthetic and natural rubber from neoprene to latex-based materials to a greater or lesser degree depending on various admixtures. Ozone is pretty much everywhere there are motors, electrical parts that switch on and off, lightening, automobiles, fuel-fired systems and more.

b) UV - Any rubber material as above exposed to UV will gradually dry out, or even melt as the hardeners are compromised. Some materials are an amalgam of celluloid based components and rubber components that will also decay very quickly when exposed to UV. Remember celluloid doll heads and other toys shrinking and crumbling over time.

c) Outgassing - many products made from natural and man-made materials, especially odd mixes as were commonly used 'back in the day' are prone to outgassing as well as some level of oxidation, even if not vulnerable to UV or Ozone. The most obvious of these is Catalin, a pre-Bakelite product that is made from the same basic ingredients, but without the aggregates (typically carbon-black, lignen (sawdust) and other stabilizers. Many soft rubbers used as platens were made from specialized mixtures with peculiar admixtures to give them specific properties. Which evaporated over time - sometimes (as with catalin) a very, very long time.

Chemical restorers attempt to undo/repair damage by replacing volatiles. That is about all that can be done without adding non-OEM materials. The ideal is to stay ahead of the damage rather than to try and recover once started.

This, in some ways, is similar to White Metal disease, which is due to environmental exposure to trace amounts of such things as formaldehyde - present (back in the day) in insulation, glues, plywood and much more. It is a matter of specific material, types of exposure, local environmental conditions and several other factors, no single one being the single cause.

Peter Wieck
Melrose Park, PA