The 'pinholing' in my glazes on the carved pieces is a concern. Pinholing is usually seen as glaze problem. Harry Fraser (in Ceramic Faults and Their Remedies 2nd edition 2005 published by A&C Black) details both ceramic body and glaze problems that cause pinholing. They range from poor clay preparation, contaminants on or in the body through to constituents in the glaze (including glaze thickener) glaze application and firing technique. Fortunately I do not have to consider every single one of these possibilities. These two pairs were made of the same clay, bisque fired to the same temperature and glazed at the same time with exactly the same glaze, brushed on with the same brush. Pinholing does not appear to happen on the 'dotted' spheres, only the carved ones. The glaze seems a little thinner on the carved pieces but enough to cause the problem? During brush glaze application is was often had to get the glaze into the dots and this may have resulted in more layers going on each area. On the other hand I had to take care to get the glaze into all the carved channels which would have had a similar effect. The glaze seemed to leave small gaps on the carved forms . Was this due to the surface? The dotted ones have been burnished prior to impressing. The carved ones, by the action of dragging a tool across and through the surface, had linear scratch marks and holes where the grog had been lifted out. Reviewing earlier spheres, where I had 'smoothed' with a wet sponge (creating slip on the surface), there were no micro holes - but instead a more gritty surface as some of the slip had been removed leaving the grog standing proud. Glaze however mostly smoothed them over, even on craft crank as on this example. this piece did have a very thin layer of copper carbonate slip brushed over and re-bisqued prior to glazing with yellow. What are the possible remedies? Comments and concerns
I could 1.coat with slip and refire. adding slip at this stage can be a problem, though used successfully by Annie Peaker. 2.spray the piece or even dip it water to make it less absorbent prior to glazing. Tried this, did not work. 3.try burnishing the surface at leather hard. Time consuming and difficult to do all over 4.damp wipe at leather hard, taking care not to lift the grog. May not be enough unless really wet 5.wet wipe as before on dry greenware then slowly dry. Concerns expressed that doing this previously contributed to cracks 6.put a thicker layer of glaze on the carved forms. Does not appear to help the pinholing 7.trying a very thin base layer of glaze before main glazing hoping to fill the holes. This helps but does not eliminate the problem and may need a combination - perhaps 4 then 3 and 7. Testing is required.
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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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