What are glazes made out of?
    Glazes are made out of all different types of materials and chemicals.  They are made out of compounds of glass forming minerals that fuse in the heat of the kiln and adhere to the clay coating it with a thin layer of glass. Some of the main ingrediants in ceramic glazes are Copper Carbonate, Borax, and Colemanite. These are only a couple of ingrediants out of the hundreds used in glazes. The tones and brightness of the colors are derived from the different chemicals used in the recipe.  The ingrediants in the glaze recipes are kind of like the ingrediants in cookie recipes, for example, a peanut butter cookie tastes a lot different than a peanut butter chocolate chip cookie. Adding or subtracting the chemicals used in glazes can effect everything in how it turns out. 
     Silica is often found in glazes, it is a chemical that is used in making glass.  Before the silica can be used it has to be liquifide and then other chemicals are added to it to form a glaze.      
     
What are some of these chemicals?

Feldspar, Any group of rock-forming minerals containing silicates of aluminum, along with potassium, sodium, calcium, and occasionally barium. 
Borax, also known as Hydrated Sodium Borate, it is white to clear in color and takes form as a crystal with a nearly perfect cross section.
Colemanite, also known as Ca2B6O11-5H20, is white to clear in color and has a density of 2.4.  It is also very lustre.  It's  fracture is perfect and distinct.
    

Here are some examples of glaze recipes:

Hawaiian Blue                                                                                Copper Red
Gertsley Borate- 80%                                                                         Nepheline syenite- 25%
Synthetic Bone Ash- 20%                                                                   Flint- 14%
Copper Carbonate- 5%                                                                      Whiting- 12%
Colbalt Carbonate- 2.5%                                                                    EPK-7%
Tin Oxide- 1.3%                                                                                  Bentonite-1.5%
                                                                                                           Copper Carbonate- .5%
                                                                                                           Copper Oxide- 2.5%
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