Looking for a good base glaze over July and August, my next trials were with 'Emmanuel Cooper Barium Matt' using the oxides recommended in Linda Bloomfield's book, and two of my high temperature stains, yellow and red, hoping to get yellow and orange glazes. Those tiles that looked a nice colour were pitted and runny , definitely not matt, whilst the stains fired out altogether. They had been fired in Test Kiln 6 set at 1245, so probably reaching 1260 with a 5 minute soak -so I have abandoned that glaze. The next trial was of another Emanuel Cooper recipe: Semi Stiff Clear Base Glaze, again with oxides and stains. The recommendation was to apply thinly but these were disappointingly dull and watery. More thoughts on glazes! Just to recap, my ideal glaze range should
I reviewed the glaze tests done already and decided to try a modification of recipe suggested by Dave. The results were variable. The blues and greens were generally best but I am keen to have colours which contrast with the surrounding vegetation, to include oranges and red. I tried a series of oxides as well as the stains with the 'UCLan Transparent' recipe. The 'UcLan transparent ' glaze is 25 cornish stone 25 china clay 25 whiting 25 flint this recipe will fire as high as 1300 Having read that particle size can affect colour and not just evenness, I sieved the base glaze through both grade 60 and 100 sieves, and the test glazes through 80 and 120. They were all fired to cone 8. Some of them worked well, some not. In particular the ones with rutile were dull and pitted. I tried a further series of oxide combinations and we fired them higher to 1300deg C. Colours were brighter and better but they showed a tendency to run. Oh dear. I did some reading, took some advice, and tried a base recipe containing dolomite 10 and bentonite 3. It was horrible to make, clumping even after sieving through a 100 mesh, and the glazes were thin and flat even when fired again at 1290. I discovered the Glazy website! This is a free to use website where you must register and sign in. Potters post their glaze recipes and preferably a picture. It will act as a website library and a place to record your own recipes. The website analyses the recipe and will give both the amount of the molecular components and also where the glaze should sit on the Stull chart. You can then increase / decrease percentage components or add more and see whether and how its position on the chart changes -ie whether the change should make the glaze more glossy etc. Unfortunately I cannot yet work out how to factor in glaze firing temperatures. Next version of the glaze (UcA2) had less dolomite and no bentonite and was poured on to the tiles. The green (copper 4, cobalt 0.15) was nice but the other 9 were very matt and showed pitting and crawling . Was it because the glaze was too thick? The tiles dirty? Because I had used Ashraf Hanna clay? So I tried the glazes again, brushing onto Ashraf Hanna fragments and they did not crawl but were still unattractive. More reading. The aim is for a glaze firing at cone 8 or below, as this puts less strain on the clay and the kiln, and thus is more sustainable . The next version has 5% talc which is predominantly silica and magnesium oxides with some calcium and aluminium. The CTM website stated that in amounts up to 5% it can improve maturity and melting of a glaze. They also advised that it should be thoroughly dispersed in water before adding to the glaze recipe.
Fingers crossed.
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AuthorI am indulging my passion for ceramics by undertaking studies for an MA at UCLAN Archives
August 2021
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