June 25, 2012 § Leave a comment
I am, finally, a happy man… For those of you that read this blog regularly, you may have noticed that I have had an issue with some of my glazes. I have had a problem with pinholes – and I have been trying to remedy it for what seems like an age, reading about it, talking to people (anyone who might listen…) and experimenting. It had become a bit of an obsession because I couldn’t find a solution, no matter what I tried.
On advice from books and people I spoke to, I tried soaking at the top temperature; applying the glaze more thickly; more thinly; adding zinc oxide; exchanging Wollastonite for Whiting… Nothing seemed to make any difference – the pinholes remained. I spoke with a number of people about it at The British Craft Trade Fair thinking that someone was bound to say, ‘Oh yes, you just need to do such and such’… George Ormerod thought that it might be something to do with the turned surface of the bowl. The pinholes are only evident on the outside of the bowls, not the inside or on any other form, inside or out.
Well, it turns out that he was right. Dianne Cross and Gill Smith said the same thing.
This is the surface I was leaving after turning the bowls. You can see that there is not an even surface for the glaze to adhere to. Dianne recommended using a kidney to rub it down after turning, or spraying a tiny amount of water onto the bowl and rubbing it with the kidney – this reasserts the skin of the clay.
My solution has been to sponge the surface down when the bowl is dry. The surface is not smooth but it is even, and it works a treat. I sponge my other pots down when they are dry to remove any finger marks and it was this that gave me the idea. Just a light sponge does the trick, otherwise the surface becomes very rough.
According to Bernard Leach in ‘A Potter’s Book’, the other thing you can do, if you only have a few pinholes, is fill in each one with a spot of glaze, then rub the spots off when they are dry. This works well, also.
The issue with pinholes is really only with the high gloss green/black glaze. I feel that because of the gloss the surface needs to be even and blemish-free. I have a new glaze, this blue glaze, where the pinholes show through as yellow under the blue, which adds beautifully to the overall patina.
It is such a relief to have found a solution to this thorny issue. The ‘p’ word is no longer on the tip of my tongue…