I want to cast a large (8-10″) sphere to use as a fountain topper. Can I cast it in a glass light fixture dome and simply break the glass after to de-mold? I can’t find reusable sphere molds larger than 4″ or so, and frankly don’t need to make many. I’m thinking to do multiple coats on entire inside (rolling it around) OR leaving glass mold in same position and pouring a few ounces at a time until nearly full. If I use a demolding agent, what should I use and can I just break the glass away when done?