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Hello, I am thinking of buying a small female torso mold, but have no idea how to go about calculating how much glass to use to fill it. Nor do I know if I should use small glass pieces or frit, ( coarse, medium or fine? ) in other words I don't know anything at all really!!!
Can someone advise me. Thank you.

Get a container. Put water in it. Mark the level of the water. Pour some water into the mold. Mark the new, lower level of the water. Now fill the container with glass until the water raises to the original level (the first mark). That's how much glass you need.

The smaller the pieces of glass you use, the more air bubbles and the less clear the final piece will be. Larger pieces, fewer bubbles, more clarity.

Do a test before you do the big piece.

Oh thank you that sounds simple, I was overwhelmed with some people’s math solutions. How can you do a test before the big piece, if you can’t use the mold? My mold isn’t too big though.

What you want to test is what the glass will look like. Small frit vs large frit, for example, will look very different. And different colors as well.

Basically, before you spend a lot of money on glass, spend a little money with a smaller mold to make sure the color and transparency will be what you want.

(You don't say what size the mold is, but if it's really small (a few inches) then you can probably just skip the testing part and make several castings with different materials. But if it's any size at all, testing is a good idea.)

Thank you my mold is only about 8” so I will practice.