Making a mould from polymorph

Polymorph is the brand name for thermo-setting plastic pellets. These things have been around for a few years, but they're still amazing for any "hacker" to have in their kit of cool stuff. We used some a while back to create terrain bases for some 28mm miniatures. The stuff is dead easy to use, and captures an incredible amount of detail.

It also has the advantage of resisting almost anything sticking to it.
And its' completely reusable - made a mould that doesn't work? Simply melt the plastic down again and try again. Finished with the mould after casting a few shapes? Throw it in some hot water and re-shape it for another project!

As it's almost infinitely re-usable, and since we're likely to need quite a volume of it to create relatively large castings, it seemed sensible to order 4kg of the stuff. It seemed sensible, until it arrived!

Now we've a couple of massive bags of polymorph, it's time to put it to the test!
Firstly, boil it up in some hot water and create a large, gooey lump.

While it's still warm and pliable, shape around the master shape

After 10-15 minutes, the polymorph has completely solidified and turns an opaque white

Now we simply wait for the plastic to cool fully, and demould....

Disaster! It turns out that our polymorph sticks to MDF far better than we imagined! It's a bit late now to think about what we could have used as a mould release - our beautifully laser cut and hand-shaped masters are completely destroyed!

At least our polymorph is reusable - had we made these moulds from RTV silicone, we'd just have a couple of useless lumps of (expensive) rubber by now! A sharp knife can be used to cut away the "contaminated" areas of plastic (where the mdf fibres have embedded into the plastic) and the remaining stuff simply boiled up, ready to be used again....