iandol on sat 9 aug 03
Dear Winnie,
On your first point, yes, Sodium chloride will invest itself in the =
vacant spaces in immature clay. But I would not like to say if it could =
be completely removed by repeated washing. Even if it were the clay =
would still be porous and will weep.
On your second point, Yes, there is a way to assist in overcoming the =
problem.
You have two options. The first is to go to a higher firing temperature. =
This is what I would do if the problem was of epidemic proportions. But =
since it is just the occasional pot there is another way which should =
have very little effect on the working or surface properties you =
cherish. I would incorporate an insignificant quantity of Potash Felspar =
or Muscovite (K rich) Mica into the body. This develops from "My =
Heretical Theory of Salt Glaze Chemistry" which states that Sodium =
Chloride reacts directly with the vitreous phase of a matured clay which =
contains Potassium (or Iron) in solution. Five percent would do the =
trick. It will give you a tighter body and not lower the maturing =
temperature by a significant amount.
Keep to your liner glazes if they do not suffer from salt. But if they =
are rich in Magnesium there may be cause for concern. Although I have no =
evidence to validate my ideas, I think this is a suspect material in a =
salt (NaCl) glaze situation.
Enjoy the raid.
Best regards,
Ivor Lewis. Redhill, South Australia.
| |
|
