(F Potters Guild of British Columbia 1349 Cartwright St., Granville Island Vancouver, B.C, VGH JR7 (604) 683-9623 | NEWSLETTER JUNE 1992 ISSN 6319 812x SLIPS AND ENGOBES SLIPS SLIPWARE direct application immediately after Mixtures of clay, water and colouring oxides or stains, They are usecd bo cover a clay and change its colour or texture. ENGOBES Similar to slips but generally containing less clay. They can also be composed entirely of non-clay materials and therefore cannot be called slips. SLIP GLAZES Glazes which contain more than 50% of clay and generally applied toraw unfired ware. CASTING SLIP A deflocculated suspension of clay in water used for casting in plaster maids. This type of slip has a much lower water content, Traditionally earthenware pottery. Decorated with colour slips under a lransparent lead glaze. SELF-GLAZING Engobes which have enougt flux to cause (hem to fire ENGOBES to a cull sheen, SLIPS Simple slips can be made by adding oxides or stains to the same clay which is being used to make the piece. They must be applied to the damp clay be- cause they have a similar shrinkage. Failure to do this will result in surfaces which crack and peel away on drying. The only colours which are possible are those which are darker than the original body. Slips of this type work very well for ENGOBE COMPOSITIONS Temperaiure Cone Cone Cone Range — o8-1 1-4 6-11 ; aus of ware es y a 2 cre” Gs Fos dts | Kaolin 25 15 5 25 i5 | 23 15 5 Ball clay 25 15 15 25 15 15 25 15 15 Calcined Kaolin 20 20 20 20 20 20 Leadless frit 15 15 15 5 3 Nepheline syenite 15 13 20 5 Feldspar 20 20 20 Tale 5 3S 15 5 3 5 Flint 20 20 20 20 20 20 20 20 20 Zircopax 5 3 5 5 3 5 Borax 5 5 5 5 5 5 «from Dante] Rhodes, Clay + Glazes for the Potter, Chilton Book Co., Philadephia, 1957, p. 161 throwing or handbuilding. Some desir- able properties are: 1. To cover surfaces with a suitably dense coating of the desirable colour. 2. To cling to the surface during the shrinkage which accompanies dry- ing and firing. 3. To vitrify at a temperature similar or lower than the maturing tempera- ture of the clay. 4. To survive under the glaze without being dissolved. ENGOHES The disadvantages of slips may be over- come by making up engobes which have less shrinkage than the clay upon which they are being applied using light burn- ing materials so they are essentially white unless coloured by adding oxides. Continued on Page 10 JEFF OESTREICH WORKSHOP Friday July 10th 7:30pm Gallery of B.C, Ceramics Slides, discussion and display of his work Saturday July 11th, 10—4 Kwantlen College, Surrey Ceramics Department Space for this session is still available. See Registration Form on p. Ll. Cathi Jefferson will have a pot luck party at her house in North Vancouver following the Saturday session.