TechnoTip Changing the Firing ‘Temperature of a Glaze Method 1: Transplant Mechanisms At the risk of negating most of what I have just said, identify the mechanisms in the glaze and transplant them into a good base glaze for cone 6 that has similar surface texture, Answer these questions: * What gives if the colour? Is it a stain, a metal oxide, a stained clay or mineral? Put this material in a cone 6 base. Note how- ever that you need to think about whether a colour depends on a sympathetic chem- istry in the base glaze. Many stains, for example, require that the base glaze be zine or magnesia free, Others require the presence of a certain amount of CaQ, * Is the glaze opaque or transparent? IE it is light in colour on the edges, then it is likely transparent or partly opaque. If it 1s adeep and vibrant colour, itis likely trans- parent. If it is a pastel colour, it is likely opaque. If it contains an opacifier like tin oxide or zircopax, then transplant it into the cone 6 recipe. CLAY STAMP ! Custen) flet Stepps tor clay é& paper by Tony Hansen * is the glaze variegated or mottled? If the effect is arceult of the presence of rutile or titanium, then transplant either material into the cone 6 glaze. * Does the glaze have speckles that are a product of a granular or enground mate- rial? If so transplant these contributors inte the mew recipe. There are other factors that are not as easy to traneplant. These often relate to visual effects in glazes that are very fluid or tunny. For example glazes that form small of large crystals of a crystal mesh across sections of the surface during cooling need to have very fluid melt. Often matte glazes are actually over fired come 6 or 8 glossy glazes that have completely crystallized, For this type of glaze you will need to have an equally fluid melt in the cone 6 range to transplant things inte (it neexts to melt well below cone 6, ¢.g. cone 2). Not easy, since getting a glaze to melt that low means removing much of the low expansion silica and alumina; that means crazing. Another mechanism that is mot easy to transplant is the character of the surface. Dolomite matte glazes, for example, have 4 pleasant silky surface that is a product of what CaQ and MgO do around cone 10 in the right hast glaze. Obviously you cannot transplant this type of mechanism. You must create or find a base that already has the surface you want (or adjust one that is close since matencss is a product of glaze chemistry; that is, the mix of oxides it comains). Fortunately, at come 6 alumina, calcia and magnesia mattes are all possible as they are at cone 10, Mcthod 2: Add the Magic Oxide The magic oxide to add is boron. The reason baron is sech an ideal additive is that it is more than 4 flux; it is a glass like silica yet it melts low, This is marvelous stuff for this purpose. One of the beauties of boron is that itis compatible with mast colourant, matte and variegation mecha- nisms. But there is another even more continned an page 9 Turkey @) Our design or September 15 - October 6, 2003 21 days From your own Denys James and Erdogan Gulec design Istanbul, Ankara, Cappadoccia Studio experience and tours % On transparent rubber Thalland mounted on clear December 11-29, 2003 18 Days acty lic Denys James, Louis Katz, and Suwanee Natewong @) Tour of folk pottenes, ternples, traditional arts and crafts Any size Tuscany, italy W Interchangeable May 14-31, 2004 17 days Denys James, Giovanni Cimatti, and Pietro Maddalena (@ Inexpensive Studio experience, terra sigillata workshop with Italian master : 1 isin Design Tours of San Gimignano, Florence, Siena | “lorichte fesents information and Registration COLOR ere menden ip 4% Denys James (6076624146 ao” Phone 250.537.4906 tlaudasepovia() thaw ca ye Website:-www.denysjames.com