Pottery and Ceramics Glaze
Glaze Info
Glaze is a thin layer of glass that sticks to the clay.
Glazes are fired at various temperatures, watch the labels for cone numbers.
Firing at the wrong temperature can produce an off effect.
The interface is a layer between the glaze and the clay that is made up of elements of both.
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All About Pottery Glazes
Glazes are made up of basically three components:
Glassformer |
Refractory |
Flux |
These three components react to each other in the heat of the kiln to make a glaze and each has a specific job to do:
GLASSFORMER
This is the material that actually becomes glass.Silica is the only glassformer used.
It has an extremely high melting temperature.
Silica is found in sand, quartz, feldspar, clay and other minerals.
REFRACTORIES
A refractory is any material with a high melting point.Silica has a high melting point, so it is both a glassformer and a refractory.
Silica is used in a glaze primarily for its glass forming properties.
Alumina is the element most used in glazes for its refractory properties.
Clay is the most common source of these elements.
Clay is made up of both silica and alumina, plus water and lots of other good stuff.
Clay increases the melted glaze’s viscosity so that it doesn’t melt into a thin liquid which would run off of the pottery and ceramic.
Clay also keeps the raw glaze materials in suspension when mixed with water.
FLUXES
Fluxes are materials which are used to lower the melting point of silica to a temperature that is practically attainable in the kiln such as, 1472˚ F to 2404˚ F.
There are many elements used as fluxes.
Some which we use in our glazes here are:
Sodium |
Potassium |
Calcium |
Boron |
Lead |
Barium |
Zinc |
Magnesium |
The above elements are found in the following compounds:
Whiting or calcium carbonate
for calcium.Dolomite
for calcium and magnesium.Barium Carbonate
for barium, which is toxic!Zinc Oxide
for zincGerstley Borate
for boron.FELDSPARS
Feldspars contain all three components of a glaze, the glassformer, silica, the refractory, alumina and several fluxes such as sodium, potassium, calcium, boron.
Salt for sodium.
The materials selected to be used in a glaze are mixed together as powders.
Then water is added to make a mixture the consistency of cream, it is then strained through a strainer to make sure it is well mixed and there are no lumps or chunks.
The glaze is then put onto clean bisqueware.
This can be done by spraying, painting, or dipping our pottery or ceramic into a bucket of glaze.
The glaze sticks to the porous bisque fired clay.
The glazed pottery or ceramic is then loaded into the kiln and fire to the specific temperature at which the glaze mixture will melt just enough to form a layer of glass, but not run off the pottery or ceramic.
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