WarmGlass.com

I have heard or read that you can carve a fire brick and cast into it.
I carved some sea shells into the brick so when cast, it would be like a relief.
Do I just fill with frit, or chunks, or do I have to make a paste??
What do you need to do for prep??
What type of schedule would I use? I assume it will take quite a long time to cool down.
Sorry if it seems like a stupid question, but I can't find anything in searches.
Thanks in advance for your input!!!!

Be forewarned that fire bricks are extremely prone to sticking to glass. I have no idea what the relative COE of bricks are to glass.

Not stupid questions, at all. First, when you carve it, wear a mask because the dust is nasty. And use gloves--the grit from a firebrick really dries out my hands.

Second, you'll need to put a release on the firebrick (like kilnwash) or the glass will stick. This can actually be a good thing, because firebrick is a bit coarse and if you work with the kilnwash a little, you can use it to refine the detail in your design.

Third, if you make undercuts in your design (where the glass doesn't have a clear, unobstructed exit path), you'll need to destroy your mold to get the glass out.

Fourth--any form of glass that will fit in the mold will work, and all the usual fusing rules (compatibility, reactivity, volume) apply. Powder will trap lots of bubbles and look translucent or opaque; billet will give you the clearest, most bubble-free look. If the volume is very great the firing schedule may take longer than you think, especially if you have to settle the glass into the detail.

Fifth, I haven't messed that much with firebrick casting because it doesn't take the kind of detail I love. When I have, though, the softness of the brick works in my favor, since it's not as strong as the glass and will tend to crumple away instead of break the glass. And since it's porous, potential air traps in the design aren't quite the issue they would be in a harder mold--the air seems to seep out through the pores.

My first thought was that firebrick is pretty hole-y...I'd be afraid the glass would seep into all the little holes and the resulting piece might look like it has little mushrooms sprouting all over it...??? Not to mention potentially locking the glass into the brick. I'd try a piece with scrap glass before risking the mold you've spent time on.

Thanks for the remarks, guys... Cynthia, good information... its just a couple of seashells and a starfish. No undercuts, lack of fine detail doesn't matter, as they will look tumbled!!! I kind of figured I'd rub kiln wash onto the holes to fill. I'll give it a shot!! Any special schedule to do this?
Thanks for the help everyone!

Thanks for the remarks, guys... Cynthia, good information... its just a couple of seashells and a starfish. No undercuts, lack of fine detail doesn't matter, as they will look tumbled!!! I kind of figured I'd rub kiln wash onto the holes to fill. I'll give it a shot!! Any special schedule to do this?
Thanks for the help everyone!