Saturday, 9 March 2013

Post 79 Brown glaze trials

My search for brown has continued with trial series 7 just fired. This was the first time I've experimented with chromium, having been reluctant to use it. So this was a matter of trying to find out just what I have been missing. As well as chasing browns I also ran a group of straight greens and also had a try at chrome reds (chrome and tin).

I used three base glazes in this trial. The first is my standard Post high calcium satin matte (test tile numbers under 7-42) the next is the Post tomato red base (tile numbers up to 7-48) and then just three using a high spodumene nutmeg  recipe. I lilke the tomato base as it produces very nice buttery surfaces with a slow cool-down cycle.

38 has a little Manganese in it which always give a standard brown colour whereas RIO will ore oftern than not give a slightly red tonality.  44 and 45 have only RIO and Yellow Ochre as colourants and set up side by side you can see the red tones coming out.

In this set there are a couple with some small amoubnt of chrome and zinc. I find the zinc invariably supercharges any iron colouration. If you can filter out a little of the reflectivity from a couple of these they are very similar. I really like 7-39 as a candidate to replicate the unglazed colouration frequently achieved in asian pots used with conifers.

The above two have heavy doses of both chrome and zinc - to bring zinc chromate as colourant into play and then RIO in 30 vs YO in 29. Once again the RIO gives more red tones and the YO more orange. Both of these offer good strong colours.

27 has a little cobalt as well as the RIO, zinc and chrome and has produced a little speckle and interesting bronzy tone which will be a very useful colour. Tile 40 againb shows the impact of a little manganese. It also has rutile but I think in this case has clouded the colour and it would bhave been better without it.

The last three are the nutmeg base tiles, with variations of RIO, YO and Tin Oxide. A wider testing of thes combinations would be useful. The colour of the darker red tones is pure rusty steel. 7-50 with just 2% iron and 3% tin is a great offwhite breakin red. In this one I mixed the RIO after sieving the glaze and so some larger particles produced nice spotting - a useful this to remember and one to put on a pot sometime.

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