| The next item on the agenda was Charles' proposed
experiment to modify his artificial ash glaze for raw glazing by adding
ball clay or china clay. Di agreed to write to the Ceramic Review
asking if other readers have used this artificial ash glaze (CR 196)
which we find reacts to give particularly pleasing response with
colouring oxides, asking for feedback.
A short discussion on food safety and ceramics followed with the
general consensus being that oxides are unlikely to leach out if pots
are fired to stoneware temperatures. Barium oxide is of course
particularly harmful for pots and should not come into contact with food
at all. Di had had a problem with a copper glaze coming into
contact with the citric acid of raspberries resulting with a heavily
stained dish.
Finally we discussed crazing which is a problem affecting most of us
at some stage. Edna had brought a crazed bowl with an earthenware
glaze over a stoneware body fired to 1040C. It was felt that the
crazing was because the two were not compatible. Suggested
remedies followed: a) firing to a higher bisque with top bungs left out
until top temperature to eliminate all volatiles from the clay body, b)
soaking at peak bisque temperature for up to an hour, c) the addition of
extra silica to the glaze to reduce its expansion, d) incorporating some
talc into the earthenware body recipes, e) substitute alkaline frits
with borax or lead frits.
Glaze Group meetings are held at the home of Diana Carter
on the second Tuesday of every other month. The next meetings
will be on 12th October and 14th December at 1.00pm. Bring
a contribution to a potter's lunch and please let Charles Stileman
(01794 340193) or Diana Carter (01962 777297) know if you are coming. |
