Sunday, July 6, 2008

Next up a slip test

I still haven't gotten a chance to get back in the studio after the raku firing. Once I do get back I have a couple tests planned; a line test with an iron red, a line test with a strontium base glaze varying the amount of colorant trying to get a nice purple. And now I am adding another test, a glassy slip test.

The idea is kind of the merger of two ideas. I see a lot of glass art. In the Pacific Northwest, home of Dale Chihuly we see a ton of Chihuly inspired glass artists. I love some of the techniques. I often see a glass form with a bead or tube of glass "wrapped" around it. This is a pretty common technique and can be visually pleasing.

I was reading a book about glazes and saw a small section on glassy slips. And a light went off, use the glassy slip to get the same effect seen on all the glass forms.

So I am after a transparent glassy slip. I want it to be stiff enough at cone 6 so that when I apply it from a syringe it will keep it's round shape. Lastly, it has to take color well. I'd prefer to use stains for this application. That means a calcium level about 12%.

Here are the base recipes I got from the book I was reading:

Gerstley Borate 90.5
Bentonite 10.5

I think this is going to be too fluid at cone 6 to hold the shape I want. So as a starting point I am going to cut the flux in half and replace it with silica.

Gerstley Borate 45.2
Silica 45.3
Bentonite 10.5

The calcium is a wee bit low for the optimal commercial stain range. So I am going to cut the bentonite in half and replace it with whiting.

Gerstley Borate 45.2
Silica 45.3
Bentonite 5.2
Whiting 5.3

This looks just about right, 13% calcium. I'm not sure about the melting point but I *think* it should be right. I also think it should be transparent. I'll make a test batch and add 10% stain (probably red) and test it in my next glaze firing.

1 comment:

synergynewzealand said...

he thanks eric great to find someone who shares their experience, Ive just returned to clay after 20 years 12 as a glass caster and I realised how much I don't remember so thanks Raewyn Synergy Glass and Clay Design NZ