Sounds interesting -

I would like to try this - but could not find it on the internet - (not sure about spelling)

GUTTA-PURSHA MOLDS:

Purchase a sheet of GUTTA-PERCHA, about one-fourth of an inch thick. Cut it about size desired. Soak it in NAPTHA (which causes it to swell), then soak it in hot water. This makes the sheet of Gutta-Percha soft and mushy in appearance, somewhat like a wet rag. Then in this condition, press it against your model, slowly but firmly ...
ANy help - Mike

thanks for the feedback I am thinking about the top one using gelatin though. I t says its ok for med to low temps how hot does tufa get I wonder. Heck I should just try it

It should be fine for tufa, at least once (tufa is pretty abrasive and may ruin the mold). If you have the ingredients, go for it!

And let us know how it works out for you. It sounds cool.

Apparently one of the first forms of latex. It's also the name of the tree which gives the latex sap.

Here is a link that might be useful: wiki link