Ehhhh I had the same thought when I saw all that steam, didn't know if it was a camera thing or.... Bummer.
I do think using your recipe for the plaster helped, much less sand than I was using previously and less water too. I'm going to try to mix a bigger batch next time in a 5gal bucket so I can do it faster.
I also need to redesign the flask I used to cast the plaster. Wood worked better than metal but I need to make it tapered so it comes out. That and better more even heat in the oven I think will get the job done.