So, my mask didn’t cure on the outside of the mould. I left it in the oven for five hours in total, and only the very limits of the mask inside the plaster and the foam that splooged out of the mould had cured.
Today I’m doing my next run, but I wondered if the foam latex inside the mould was even getting up to temperature. The oven that I’m using is our kitchen; an old Tricity Bendix that’s about thirty years old. It’s not a fan oven… and this over is never used to cook food in. We only use the hob above. Never use an oven that you’re going to cook in, as the released chemicals mean the oven is no longer food safe!
I decided to run a test.
A glass ramikin dish containing about 2cm-worth of olive oil. This is then covered over with a single layer of aluminium foil; not so much that the heat can’t get in.
I set my oven to 130C and left the oil in for twenty minutes to let it warm up.
The resulting temperature of the oil in my oven was 79C, just 6C off the 85C limit that I’ve read foam latex shouldn’t be baked over.
Now, I think the important two things are that it’s an old oven, so the thermostat might be unreliable, especially at low temperatures. Also, it’s not a fan oven, so the heat isn’t being circulated beyond simple heat convection. The parts of the foam latex that cured on my last run were both on or near the exposed areas, and they were also near the top of the oven. The total height of my life cast and mould is ~ 35cm; that’s pretty big.
If you think about cooking several things in an oven on different shelves in a non-fan oven, you know that there’s a big difference between the cooking times for the different shelves.
So… I’m going to try baking at an oven temp of 110C today.
Tip: Do an oil test in your oven, like the one I’ve done. See what temperature the oil gets to at 71C on the thermostat. It might not be anywhere near the required temperatures for baking foam latex. 75C on my oven gave an oil temperature of 62C. That’s very low and, whilst I’ve read about people baking foam latex at this level of temperature, the baking times can exceed even 6 hours.