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Wednesday, 1 July 2009

Pottery Clinic

Glaze blister at high magnification
Post your questions about any pottery or ceramic matter.

All questions are welcome regardless of how simplistic they may appear !

My commitment is to respond in a timely fashion and to provide the best advice that I am able to based on my own perspective and the information provided.

I look forward to answering your questions

2 comments:

  1. I have used grogged terracotta meant for outdoor ceramics but some of the items made after glazing and firing pitted a few days later. Why is that?

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  2. Hi Vicentlia,
    Thank you for your interesting question.I am not sure exactly what you mean by pitting. Normally pitting is seen as holes in the fired glaze or body after firing. It does not usually happen after a few days. Crazing (small cracks) caused by moisture expansion can happen up to some months later. In some cases I have seen this crazing happen near to coarse grog particles giving an impression of pitting. An easy test to see if you have moisture expansion crazing is to sit the piece in water overnight so that the piece absorbs water through the foot. This exaggerates the problem and the whole piece may craze. The 2 main issues here are glaze and body expansion and the firing. Ideally to reduce moisture expansion you can fire to a higher temperature so the fired piece is less porous and does not absorb water.

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