Making Molds with Firebrick

Firebrick is the type of brick used to make kilns, it’s a soft white refractory material that stands up to high heat. In my area, you can buy them through the local classified ads for about $3 to $5 each. I use them for a number of things, one of which is sawing into custom slump mold shapes. When doing production work, I may need 5 or 6 of one kind of simple mold at a time, and it makes sense to cut them myself if I can.


Firebricks contain silica, and are very dusty to cut. You should cut outside and ALWAYS wear a respirator when cutting fire bricks.


Firebrick Molds

Firebrick and materials

I’m cutting slump forms for business card holders today. Start by measuring how wide you want the business card holder to be, I’m using 1 1/8″.

firebrick molds

Measure fire brick

I want to cut a very slight slope in the form so it is wider at the bottom, this will ensure my glass will come off after slumping. The bottom is marked at 1 1/4″

Firebrick molds

Mark cut line

I like to draw the cutting line all the way around the brick, it helps me keep the cut straight and I can check as I go along.

Firebrick slump molds

Cut Line Around Brick

I’m using a baby hacksaw to cut the brick, but you could also use a coping saw, or a regular hacksaw. Remember to do this outside and wear a respirator. Firebricks are soft and easy to cut, but they wear your blades out fast, so keep that in mind too.

firebrick slumping mold

Cut firebrick on line

Once you’ve cut all the way through, you’ll have a form that should look like this:

firebrick slump form

Firebrick Business Card Form

The surface of the brick is way too rough to slump glass on directly, so I typically staple a piece of thin fiber paper over the form. Shelf paper isn’t thick enough, you need at least 1/32″ fiber paper.

firebrick mold

Firebrick form with fiber paper

An office stapler works fine for stapling the fiber paper on. Keep the staples close to the bottom edge so your glass doesn’t get hung up on them. The bottom edge is the wider edge.

fire brick mold

Staple on fiber paper

Once the paper is stapled on both sides, you can slump glass business card holders on it.

fire brick slump mold

Business card holders

If you are gentle with the form, you’ll be able to slump with it many times before the fiber paper has to be replaced.

firebrick business card slumper

Fused Business Card Holder