Well, the demould is done. In the words of Lady Macbeth "if it were done, best it were done quickly". It took 2
days to get the blighter out. The reason was an error of judgement earlier in the process, when I used the maximum amount of 'thixo' for the last two coats of silicone. This lead to a very "knobbly" exterior to the mould, so that putting the plaster bandage straight onto it would have been problematical. Instead I covered it with a sufficiency of plaster, and then once that was smooth-faced, followed it up with mod-roc.
This created two new problems. The first was that as the plaster dried and cracked a little - as it's won't to do - one or two little pieces migrated down between the silicone and the hard plaster, altering the shape of the casting when poured. I was very fortunate in that this only occurred in one place, and is easily dealt with. The second problem was that later on, I couldn't detach the casting and the silicone easily from the plaster/mod-roc casing, so had to demould the resin from the intact plaster/silicone mould. As the resin alone weighs some 15-20 kg, this was not easy. Had I been able to remove the cured resin cast and silicone from the plaster easily, then peeling the silicone from the resin cast would have taken seconds, not 2 days.
The silicone also had an air-tight seal on the resin. I tried injecting air with syringes - no joy. In the end I inserted 100 old lolly-sticks between the silicone and resin, and eventually reduced the area the silicone was in contact with the cured resin just enough to move one slightly in relation to the other. All the sticks were then removed, and reinserted at one end, and finally I got the bugger out. It was
one of those jobs you have to keep walking away from, as you feel the frustration building, as it would have been folly to go in with harder tools and break or score the resin.
The next job is the post-cure heat treat, but I have to make a set of supports for it, as it will only fit in the oven at a peculiar angle. A temperature probe and a good book will make the hours fly by as I babysit this thing in the oven - the temperatures are far below what my oven thermostat can achieve, so it'll have to be turned on and off using the hand-held probe as a guide.
https://www.youtube.com/watch?v=o9gEYqm3L6A, more or less covering the above.