Sunday, 21 November 2021

Refractory Mould – Nuts & Bolts

The first thing I had to do for this project was to create textures in a block of clay.


I found some screws and bolts and a wingnut and pressed them into a squared off block of clay.  I thought they would make some interesting textures – bold and easy to see what they were.

Next I built a box around my clay using Cottle boards and clamps.   Around the bottom of the boards I added a little clay so none of the plaster mix would leak out.


Plaster Recipe for refractory mould:  (to be measured up as required)

·       1lb plaster powder

·       1lb molochite powder

1 pint water

Once the plaster mould was dry, I could gently remove all of the clay.

I washed off all the tiny remaining bits with a toothbrush and water.

The next job was to fill the mould with water and measure it.


It’s important to do this BEFORE the mould is put in to the drying cupboard as doing it afterwards would allow the mould to absorb more water, causing issues in the kiln.

I scratched on the side the amount of water needed to fill it – 260ml.

The mould then went into the drying cupboard for about a week to make sure it was thouroughly dried. 

Now it was time to work out how much glass I needed.

A = the amount of water that fills the mould

A x 2.5 = the weight of glass needed to fill the cavity.

So this one was 260 x 2.5 = 650 grams

I weighed this amount out and positioned it into the mould.

Finally the mould and glass went into the kiln so the glass could melt into all of the crevices.

Once out of the kiln I could gently break away and discard the mould material, leaving the slab of glass.


I have put a little too much glass in this mould, hence the overflow, but it will be interesting to cold work it to bring it back to shape.

I used the flat bed grinder in the coldshop to grind all of the excess glass off this piece. I used 120 grit at first, moving on to 320 grit once I had the shape I liked.

I actually had to stop at that point as I could see some stress in the corner of the piece which I suspect would have chipped the corner off if I had continued.

Still,  I am rather pleased with the result, and cannot wait to have another go.

No comments:

Post a Comment

I would love to hear from you, questions, comments and salutations all welcome.