clay molds for glass casting by Kristin Gudjonsdottir

Clay Molds

The Coil Way

The molds were coil built.

bisked fired (1600F - cone 012 ) and glass frit put in.

These molds were made in 1993 for Ancient Forms and were the first molds that I did useing clay as the mold. I didn't put any kilnwash on the inside of the molds and just filled them up with crushed up glass from my recycle bin (the trash) at school. At that time the glass department was useing Gabbert cullet. I found out later that it and Louie glass cullet react very simmilar to my clay molds. I rarely have to put kilnwash on the inside for thouse glass types. they didn't seem to stick except if I had alot of oxides mixed in with the glass or had intentionally made the surface rough like you can see in Pink Form made with Louie glass

The Lost Paper Casting

Wet postage size paper (your junk mail and egg cartons are great ) over night or if you don't have time to do that just make sure you have paper that absorbs water fast like egg cartons and newspaper.

Put the pulp in a blender with lots of water so you don't overheat you blender. Scoop some of the grinded paper on to a flat sif like you are making paper sheets this is to get most of the water out and then press on it also with your hands flat or some board to get more water out. Then take carefully parts of it off and place it on the piece that you are molding from.

Picture shows two paper molds. See how I have open it to get the piece out that I had molded the paper around.

Finished mold. I had covered a rubber tube with the papermache. when the paper was dry I cut it open, got the tube out, closed the papermold again and molded the clay around it.

Form the wet paper around something. Cut it open when it is completly dry and take out the thing that created the form.

Close the paper form again ( I use E 6000 glue from a craft store) and put the clay around it. Make sure you have an opening.When the clay is dry. Bake (bisk) the clay and you have a mold. I always bisk the clay to the temperature that the glass is going to be cooked in it. That way I hopeing that the clay is not going to shrink more if I have underfired the clay compared to the glass. It seems logocal and it works.

You can skip the paper and form the clay directly around your desired form and cut it off when it is leather hard and put the clay parts together again. Don't forget to put the sprue part on to hold more glass then just the mold will, for the mold will need more when glass starts to melt.

Picture shows a finished mold and the plastic toy I used to create it.

Here I also make it with the paper.

The surface of the glass is going to be different. More like you see the papermache form. Doing it straight over the plastic form will give you a smoother surface.

I did cast some baby jars into the smoother form. I had never done that before and everthing came out super divitrified. I also ran out of jars ( I was so sure I had enauch!) so the mold didn't fill up all the way. Live and learn. So the next one is waiting to be fired with some glass I know how behaves as soon as I will make some thick castings in my big kiln again. Right now it is little cones over and over.

A little test in making glass legs with a clay mold