Glaze Group Meeting

12th April 2005

Crystalline Glazes

Mike reported some unsuccessful attempts to make his crystalline, cone 6 recipe with the unity formula of Ferro Frit 3110 made up from soda, quartz and whiting (did not fuse at 1230 C), and with lithium replacing sodium (glaze completely shivered off test pot).  Alison will fire the sodium-based glaze to 1300C with one of her "porcelain runs" to test the formation of fused silicates at higher temperature.

Mike found the crystalline glazes dissolved foot rings made from white insulating brick - causing pots to topple during firing and fuse together in a "creative pile". A more reliable method of dealing with glaze runs will be sought.

Crystalline glazes were viewed in ultra violet radiation from a sun lamp and the dramatic fluorescence of the zinc silicate crystals noted with interest.

Coloured clay

Following Jo Connell's demonstration, Di had made coloured clays from body stains and Scarva Earthstone Original in powder form.  The colours obtained were even, soft tones.  Brighter colours were obtained in tests using copper oxide and cobalt oxide as colourants.  When fired to 1120C the copper green diffused slightly into the surrounding white base body.

Di is to "go to work on an egg" shape with coloured clays next and also will experiment with coloured slips trailed into moulds with white slip used on top.  Maybe this will produce effects similar to those obtained by impressing rolled strips of coloured clay.

Glaze Testing

Alison has finished researching this and has used Leicester County Council laboratories to analyse one of her lead bisilicate - earthenware glazes.  There was some interesting discussion on the need for studio potters to use this testing and Alison will prepare a separate report in a future Newsletter.

Raw Glazing

Charles has encountered glaze - lifting when using a raw glaze (higher clay content) artificial ash glaze and believes that the glaze was applied to too dry a surface so that it was not "wetted" sufficiently.  He will repeat his test using damper pots and also test the use of Courgel/c.m.c. into his glaze to improve its application.

Alison has no real problems with raw glazing porcelain and follows the same firing schedule as normal glaze firing bisqued pots.  In both cases, however, she leaves the top lid ajar for the first three hours to allow the water vapour to escape thoroughly.

A.O.B.

Having opted for a break from crystal glazes, Mike has made up a reliable Oatmeal Speckly to use with the "Orange Reds".  Based on Mike Bailey's Aluminium Matts, the recipe is:  Pot. Feldspar - 70, China Clay - 16, Dolomite - 7, Whiting - 7, Yellow Ochre - 7, Tin Oxide - 6, Ilmenite - 0.5.  Electric kiln cone 6 (1230C) and needs 4 coats brushed on otherwise thin shiny tan colour produced.

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 June 2005 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.