The thread on gamboge reminded me of gutta-percha, once used for golf balls and dental fillings:

http://www.plastics-museum.com/materials/naturals/gutta.htm

ED: Can't get the link to work, don't know why. Sorry.

ED 2: Oh. It is working now. Baffling.

Dear dxb: I have been having a lo of trouble with the
server being slow. In WindowsXP I have a little "progress
meter" that shows that request has been sent to server,
but server is hanging fire.

Here's another URL, but with only a few additional facts:
http://collections.ic.gc.ca/cable/gutta.htm

One thing I didn't know is that gutta percha deteriorates
in sunlight.

I have a bunch of root canals stuffed with it. Where the
sun never shines. Here's another article, a hundred years
old, but with a lot of information:
http://www.ibiblio.org/herbmed/eclectic/kings/isonandra.html
I wonder how much polyethylene is now used on cables, as compared to teflon.