The second major function of the burn out is the investment - drying/curing. It vaporizes leaving detail in the investment to the extent guys talk about accidentally casting a finger print on something. The initial melt out gets rid of most wax but not all - especially given the molds can have all sorts of reverse curves that would not allow the wax to flow out. That is the 'burn out' and is critical for a couple of reasons. After taking the tray of wax out from under the mold, the oven is taken up to 1300F. The wax is melted out of the mold at under 300F, however this is just to preserve the wax for reuse. I'm far from expert, but have been reading about lost wax casting having recently bought a bunch of stuff. You mentioned you were going to try a pour today so i thought a friendly of caution in order. I'll be firing the foundry up a little later today to give it a shot.) Obviously, I'm going to need to make the plaster thicker on the molds, but that's going to be difficult when I'm having issues with the drying time. (Assuming it doesn't shatter when I pour the aluminum into it, I haven't done that yet. I'd rather not do it that way, as it takes a lot of plaster (several inches thick around the wax in all directions), and getting the final product out of the mold is going to be a bit difficult. That one was a massive one I made by pouring the plaster into a small plastic tub surrounding the wax model and letting it harden that way. I've got a bunch of molds made, but when I heated them to melt the wax out of them, only one of the molds didn't crack. So, is there a particular type of plaster I should buy? A better ratio of water to plaster than the one I'm using? Or is there something I can add to the existing plaster that I have to slow down the drying time? I even tried sticking one of those "As Seen on TV" Robospoons into the bowl I was mixing the plaster in, thinking that by keeping the stuff agitated, this would slow down the hardening process. If I increase the amount of water (1:1 plaster to water, or 1:2, p-2-w, or even higher), I either get the same thing or I get a soupy mix which has trouble adhering to the wax and will literally take days to dry enough that I can begin to think of adding a second coat. I can't even get a decent single layer coating on the wax before the plaster gets too hard to be usable. What happens is that if I mix the stuff up following the directions (2:1 plaster to water), the stuff begins to set before I can even get one small wax form (think Hot Wheels/Matchbox car, with a short, thick candle stuck to one side) coated in a single layer. I'm having a bit of an issue figuring out what should be the right mixture of water-to-plaster ratio, or if there's something that I could/should be adding to the plaster.
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