The commonest type of glaze is that which is made from ready prepared, commercial substances. These are called raw glazes as being made from raw materials or materials which need no preparation.

It is possible to mix a glaze in a druggist's mortar by hand, using fine sieves, but if the best results are to be secured, a small mill must be used for grinding. The best form of mill is the ball mill or jar mill. This consists of a porcelain jar which is set in a frame and made to revolve upon its axis in a horizontal position. It is about half filled with porcelain balls and these as they roll against each other perform the grinding. These mills may be purchased ready for use, either as a single jar to be worked by hand or a battery of two or more revolved by power.[L]

A good pair of scales is a necessity and it will be found convenient to use metric weights which need no calculation into pounds and ounces. Suspended scales are not as easy to use as the form known as counter scales or balances. They should have movable pans which are usually nickel plated. Upon these the materials can be placed direct without the use of pieces of paper, which are always troublesome and inaccurate. There should be a graduated bar on the front for the adjustment of weights of five grams and under. This avoids the use of small weights which are always being mislaid and lost. Dealers in chemical supplies keep these scales in stock and the cost is about eight dollars. A set of weights must also be procured from one hundred grams to five grams inclusive. These need not be of the accurate adjustment which are used in analysis. A good inexpensive grade is sufficient.

The ingredients for glazes are given in the following list:

Commercial NameChemical NameSymbol or FormulaEquivalent Weight
White LeadLead CarbonatePb(OH)2 2PbCO3258
Zinc OxideZinc OxideZnO81
Soda AshSodium CarbonateNa2CO3106
NiterPotassium NitrateKNO3202
WhitingCalcium Carbonate (Carbonate of Lime)CaCO3100
FeldsparOrthoclaseK2O, Al2O3, 6SiO2557
Kaolin or China ClayAluminum SilicateAl2O3, 2SiO2, 2H2O258
FlintSilicaSiO260
BoraxSodium di BorateNa2B4O710H2O382
Boric AcidBoric AcidB2O33H2O124

For coloring, the following metallic oxides are used:

ColorChemical NameSymbol or FormulaEquivalent Weight
BlueCobalt OxideCoO80
Blue and GreenCopper OxideCuO79
Gray and BrownNickel OxideNiO75
Brown and YellowIron OxideFe2O3160
BrownManganese CarbonateMnCO3115

Under-glaze colors may also be used for coloring glazes, the color being ground with the glaze batch.

It is not absolutely necessary to commit the formula and equivalent weight to memory. They will soon be remembered as use becomes second nature.