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First Glaze Tests!

January 4, 2013

This year I chose two Ceramic workshops, and two in Metal.  I have now finished in ceramics so will be uploading some of the exciting things I’ve been learning and making in the past two months. One of the first workshops was about mixing and testing glazes, which is much more complex than any of us realised at first.

As well as being divided into stoneware and earthenware, Glazes are made to produce certain aesthetic and functional qualities, such as shiny or matte, food safe or just purely decorative. I chose to make a simple shiny tin (White) lead-based earthenware glaze, and then added different amounts of oxides to produce different colours.

Base Glaze

This was the basic glaze. I’m happy with the results, as the colour was strong over the modelling clay and it had a nice consistent, smooth finish.

Recipe for Lead Based Tin Glaze (1080 – 1100 Degrees Celsius) 

Lead Sesqucilate   74

China Clay   20

Flint   6

Tin  5

I made 500 grams of glaze which was more than enough and gave me 50 grams of each test – as I ended up with 10 different glazes once I have mixed in all the additions to the base glaze. All of the tiles were dipped into the glaze three times – with the top part having three coats, to also test to see what is the best number of coats.

Base Plus Colbalt additions

This is the white tin base, with different amounts of colbalt oxide added to them.

(Left to right)

0.5 % colbalt added to base

1 % added

2 % added

Colbalt is one of the strongest oxides for adding colour, so I used it in small amounts. The tin did seem to make it a bit speckled even though the base glaze was sieved twice, and then twice again with each addition.

Base plus Purple Iron Oxide This is the base glaze with Purple Iron Oxide added to it.

1 % added to base

4 % added

6  % added

I was really interested to see the results of this test, as I (Stupidly) assumed that as its called purple iron oxide, that it would end up…well, purple. But this is exactly why we do tests – as it is very much brown in colour! But I am happy with the outcome, especially in the 1 % addition – it looks exactly like sand and it is beautifully grained. Even when on larger pieces and over a terracotta clay body, it still looked strong and lovely.

Base Plus Copper Oxide

This is the base glaze with Copper Oxide additions.

1 % added to base glaze mix

4 % added

6 % added

I was really pleased with these copper tests, as the 1 % was a beautiful shimmery, light green, then the 4 % was not quite saturated, so it was metallic but iridescent, and then the 6 % gave a strong saturated gun metal colour. Again, when used on larger pieces they were strong and as intended.

I also tried it on a tile over three coats of black slip, but I did not like the outcome, a it looked a little grubby over the black. I would not recommend a white glaze over a coloured slip, as it doesn’t show through very well.


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