Why we do glaze tests


I could have been weeding, hoovering, scrubbing the bath.  So I did some glaze tests and racked the kiln temperature up at inappropriate speed.

Then a waiting game: 1265, 1264, 1263, 1262 … still five hundred and odd at midnight.  I hoicked the pots out at six before a long day out, and only had time to look properly this evening.

All the same glaze:   left, usual stoneware and temperature; centre, usual stoneware and a mere 15º hotter; right, white stoneware, some firing as centre jug, a brighter green, few speckles, and small glassy bubbles I’ve not seen in this glaze before.

1 all same glaze

The scrap tiles hold the little test batches of the blue, lavender and grey glazes.  On the thinly glazed stoneware tiles they have crazed;  the thicker glaze on the porcelain tiles hasn’t.

2 crazing

3 not crazing

This is also one of the new glaze test batches.  Again, porcelain versus white stoneware, slightly thicker on stoneware, same firing. Weird little crystals.

4 crystals

The dark glaze is a commercial product, glossy but not too hard; inside, the hot blue gases have coloured the white lining glaze.

5 glossy

6 fumed blue

In an open green vessel, the identical lining glaze is almost pure white and as soft as velvet.

7 plain white

And the eccentricities of rutile seem a little brighter and more orange than usual.

8 rutile


2 responses »

  1. It’s effectively magic, to me, certainly not a science. You puts it in the kiln, and something seemingly random comes out a bit later. Those three jugs are really interesting – I can’t work out which I like best.

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