Ceramic Thermal EventsMany ceramic problems relate to a lack of understanding about what is happening at each stage of a firing, there are just so many materials that are doing so many things. This part of the database will help solve that problem. In a material-centric ceramic information universe it quickly becomes evident that each material has its own way to decomposing and melting. Many materials (especially ground minerals) have multiple decomposition events where they change crystal structure (accompanied by volume and state changes), release gases (e.g. CO2, H2O), soften and melt. This area of the knowledge base brings together all of the events in the thermal decomposition that have been defined for individual materials or minerals (however there are obviously interactions, see paragraph below). The result is a master temperature line that can be examined for any specific range to see what is happening there and specific temperature events that are linked to other parts of the database that relate to them.
One key thing to remember about studying the thermal history of how a material decomposes, alters and melts is this: In glazes and clay bodies materials interact, often they do not evolve in the same way when they are part of a mixture of other materials that is being heated. For example, barium carbonate decomposes at 1450C by itself, but in a glaze it readily dissolves in the glass melt. The story is the same with calcium and magnesium carbonate. Kaolin by itself has a very high melting temperature, but dissolves readily into active melts at low temperatures. When low melting materials are part of a glaze recipe, for example, they act as catalysts that accelerate the reactions of other materials. Also, if these catalysts create a glass phase that actively dissolves materials that normally go through complex phase and crystal changes during heatup, none of these changes ever get a change to happen because the particles have dissolved. In addition, another level of complexity arises: the product of a mix of many material will often have its own complex thermal history that exists only as that mix. For example, certain crystal species only grow where the chemistry is just right, no material may have that chemistry, but a mix can. See Also - Reducing the Firing Temperature of a Glaze From Cone 10 to 6
Moving a cone 10 high temperature glaze down to cone 5-6 can require major surgery on the recipe or the transplantation of the color and surface mechanisms into a similar cone 6 base glaze. - A Low Cost Tester of Glaze Melt Fluidity
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems. - Fluidity, Melt Fluidity
Molten glazes exhibit viscosity, that is, a tendency to run or to stay put. This is why matte glazes are referred to as stiff or viscous. The degree of fluidity is often compared using flow testers that have reservoir of glaze feeding onto an inclined runway. Glaze melt fluidity relates closely to a... - Decomposition
Most materials used in ceramics do not just simply melt when fired in a kiln, they go through one or more state changes. Most often these changes result in loss of 'volatiles'. Clays, for example, typically lose about 5-8% (can be up to 12%) of their weight during firing as CO2, H2O, SO3. Calcium ca... - Firing: What Happens to Ceramic Ware in a Firing Kiln
By understanding what sorts of change art taking place in the ware at each stage of a firing you can tune the curve and atmosphere to produce the best possible ware. - Reducing the Firing Temperature or a Cone 6 Glaze
This chapter in the lessons section of the book (and matching video at digitalfire.com) shows you how to make a melt fluidity tester and how to find out which materials in a recipe are contributing a ... - Limestone, Calcium Carbonate
Also called GCC (Ground Calcium Carbonate), limestone is a very common sedimentary rock. Calcite and Aragonite minerals are the pure crystalline forms of CaCO3 (limestone contains them), but limestone... - Feldspar Teaches Us About Formulas, LOI, Unity
The first chapter in the lessons section of the INSIGHT manual (and matching video at digitalfire.com) deals with the basics of oxides, formulas and analyses. It shows the relationship between materia... - Two Sources of CaO
This is an chapter in the book (and matching video at digitalfire.com) shows how to enter calcium carbonate into an recipe and then make sense of the LOI (Loss on Ignition) and formula weight that it ...
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