iandol on fri 24 oct 03
Perhaps the simple reason why a glaze show signs that it has not melted, =
then matured, as anticipated is that insufficient work has been done =
within the kiln. It is possible that, although a pyrometer reading =
indicates a kiln has reached the desired maturity temperature, the =
fabric of the glaze has not adsorbed sufficient energy to complete the =
chemical reactions which need to take place. These include the breakdown =
of compounds which contain gaseous elements and the dissolution of Group =
2 Alkali Earth compounds which have a profound effect on Viscosity and =
Surface Tension when they dissolve into the silica melt.
If the shelf on which a plate stands has not reached a high enough =
temperature, then the centre of a plate which stands on that shelf will =
be below the anticipated temperature. The answers seems to be... "Allow =
more time for things to happen",... "Prolong the firing",..."Use a =
shallower ramp for the heating"
Hope that helps.
Ivor Lewis. Redhill, South Australia.