I've now built up the remaining sides of the Mould box, to the desired height. I have then sprayed the inside of the box and the figure and plasticine with "formula 5" release agent, I find this helps when later separating the mould.
The moulds I'm going to make are made of Room Temperature Vulcanising rubber (RTV). The rubber comes in a thick liquid form (similar to treacle). You decant the required quantity into a small mixing tub/bowl and add drops off a catalyst which starts the reaction off. Depending on how much catalyst you add, it takes about 24hrs to set.
I'm using RTV 101 from Alec Tiranti's in the UK. The link is at the side of the Blog. The more you buy the cheaper it is, however for a mould this size (which will use about 200g of rubber in total) it will cost about £4-5 per mould.
For this first half of the mould I've mixed up about 100g of rubber with the required catalyst, make sure you mix well to ensure that the reaction works. Once mixed, I often leave it to sit for a couple of minutes, as it tends to get small air bubbles trapped in it from the mixing process which need time to work themselves out.
Ok were ready to encase our lad in his rubbery grave! hopefully an experience which he will survive.
Initially dribble a small amount of the rubber mixture over the figure and other points of detail, don't put too much on at this stage, and don't touch the surface, as this tends to make it stick. Once a light covering has been achieved, stop for a couple of minutes, to allow the rubber to spread. Again this is to try to prevent air bubbles forming on the surface of the mould.
Now pour the rest of the rubber, try to pour steadily into one corner, allowing the rubber to flow out across the box, this should prevent bubbles forming. Keep going till you've filled the box up or run out of rubber, which with about 100g should be about the same point, hopefully!
The mould now needs to be laid aside to set for 24hrs. Don't be tempted to take it apart prior to this, go and do something else, I'm off to finish that drum.
Next time, the "other half" of the Mould!