Tuesday, 16 December 2014

More about glazes                                                                                                             

  I find that clay people are quite polarized on the subject of glazes. Some love the chemistry, science and experimentation of glaze making, and others stay away from it as far as possible. Me, being the curious one, can happily spend weeks mixing and testing glazes just to see what happens,and documented tests are running into several thousands by now.
In my students days I got interested in superimposing glazes ( applying one on top of another). Most literature at the time ( and I'm not sure if that has changed) implied that if you understand the chemical composition of the glaze you can predict the way it looks. Well, that is true...to an extent. There are many more variables, which make it interesting, and ( just the touch) unpredictable... If the chemical composition of the materials was the only relevant data, you would expect that a piece with glaze "A" on top of glaze "B" looks the same as glaze "B" on top of glaze "A". After all, it all melts together. I was quite thrilled to discover that they can look quite distinctly different and thus the testing monster was created.

Couple of years ago I used a bubbly glaze on the "Gateway 21". The effect was created by applying a Crawl glaze on top of the Crater ( or Lava) glaze that I tested years ago:                                                                                                                                                   

I tried to recreate it last year for the "Shape of Thought", but something has changed and the result was quite different. Is the change in supplier of one of the ingredients the culprit? (That is why some of the glaze recipes don't travel well between the continents).
I thought that I should give it another go, with the same disappointing results.

First tile is original Crater glaze with crawl glaze on top. Second tile is Crater glaze with additional 4% of Silicon Carbide, and third tile is new Crater glaze with Crawl glaze on top. Yes, more bubbly, but very different from the original. 

Crater glaze generally contains Silicon Carbide, and crawl glaze "secret ingredient" is light Magnesium Carbonate. I have not come across glaze that combines both materials together, so I thought to give it a go:

Andrea's Fizz glaze:
Magnesium Carbonate light  25%
Nepheline Syenite                 66%
Ball Clay                                  5%
Silicon Carbide                        4%

Result is on top right, with "Fizz" on top of various dry glazes and slips on the other 3 tiles:

Here are the close ups of tests with 2 different Crawl glazes on top of the same dry glazes. I have not tested the Crawl 1 by itself as that is the glaze used on "Shape of Thought". 

I really like the lichen effect of this glaze. One of my favourites!


  1. Hallo Andrea I am delighted to have found your beautiful work I do love your Glaze especially on your gate, How high did you fire it? I m trying to develop an low fire volcanic glaze crater glaze here and is quite interesting , at the start. If you do have a any experience with a low fire crater glaze could you tell me about it?Any way keep up the the great work!!!

  2. Hi Nico,
    I fire to cone 6, 1220 Celsius, electric.
    I have seen interesting lava/crater low fire glaze here:
    Please let me know how it works out if you end up trying it
    p.s. it is worth trying both glazes on top and underneath, effects might be different