Glaze Group Meeting

8th November 2005

The meeting opened with a study of crystalline glazes, currently being explored by Mike, Diana and Rose.  Mike had created an excellent triaxial chart mapping the results of tests with his blue crystalline glaze.  By varying the amounts of frit, zinc and silica the results were clear to see.  The relationship between an increase in zinc, with less silica resulted in a duller surface and more crystals.  By increasing the silica with less zinc, a shiny surface occurred but with fewer and larger crystals.  He also had applied his white slip (80 China Clay/20 Ball Clay) onto Briar Wheels Buff stoneware clay and used a nickel-based glaze with pleasing results.

The subject of crazing and crawling was discussed again, firstly with crystalline glazes where with more crystals , less crazing was experienced by the group.  The initial check to prevent crawling is to make sure that the pot is perfectly dust free and free from any grease.  Suzanne wondered if firing to a higher temperature would eliminate this problem.

Charles mentioned that some potters add 8 to 15% Leighton Buzzard sand to their clay body to assist throwing larger pots.  He promised to research the cost for a group purchase.

Finally, it was observed by a member that natural iron oxides tended to give a plum colour whilst a synthetic form resulted in tan.

Glaze Group Meeting

10th January 2006

Crystalline glazes

Mike had done further tests using the same base glaze and heating cycle that previously that had given large blue crystals, but with 3% nickel plus 2% iron substituted for 0.3% cobalt plus 2% iron.  Although this gave large crystals, Mike was not happy with their colour or the brown background so will be carrying out further tests.  He commented that areas without crystals have the same chemical composition as the crystals but with a different arrangement of the atoms.

Black Glaze

Using the following composition downloaded from the internet, Mike showed a good shiny glazed example obtained by firing at his standard temperature of 1230C:  Potash Feldspar 72, China Clay 7, Whiting 13, Flint 8, Red iron oxide 10, and cobalt oxide 3.

Artificial Wood Ash

Charles has calculated the following recipe for his artificial ash on its own (we have in the past always used it incorporated in the glaze) and we propose to try it out hopefully as a "cone 6" glaze on our different clay bodies, without slip.

Blue Green Glaze

Charles had in the past at evening classes obtained interesting blues with the following glaze both with and without a "white" glaze on top:  Potash Feldspar 10, China Clay 45, Copper Oxide 1.0, Cobalt Oxide 0.5 and Bentonite 2.

However, fired at Cone 8 in his own electric kiln results were excessively dry.  As his trials had produced some pleasing colours we have decided to carry out further tests.

Leighton Buzzard Sand

Several potters add between 8 and 15% of grade DA 80F (dried) sand to their clay bodies.  This is now supplied by WBB Minerals (who have taken over Arnolds, the previous supplier). Tel No. 0845 357 752.

Charles had found that coarse grog added to his clay (to improve thermal shock resistance) reduced the tendency of large pots to sag during throwing.  He is about to try adding Leighton Buzzard Sand to see if this has the same effect (WBB have supplied a 1kg FOC sample).

Throwing Large Pots

It was suggested that a helpful video covering throwing by Jim Keeling of large garden pots at Whichford Pottery, Warwickshire, is available maybe for showing at the AGM (Charles has a copy).  They cost £6.00 each.  To purchase, phone 01608684416.

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 the 14th of March and 9th of May 2006 at 12 noon.  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.  Other SCG members and anyone with glaze results to share are always welcome.