The Unity formula is a way of presenting a glaze so that it can be compared to other glazes by how many molecules of each oxide are in the glazes. Glaze materials usually have multiple oxides in them and a glaze recipe may have four or more sources of silica and other oxides. Since the amount of silica in a glaze has a big impact on how the glaze looks, making sense of the separate ingredients is critical. The unity formula is the tool used most often to do this comparison.
When comparing recipes for hot chocolate I like to use a one cup serving as my standard. Strong coco will have 3 or more tablespoons of cocoa powder, normal will have 2. If you are serving cocoa to a child 1 tablespoon might be more than enough. Sweet cocoa has more than 2 tablespoons of sugar, bitter one or less. Having the recipes written per one cup serving helps keep things easy to compare. I like to use about 1 teaspoon or less. These are comparison based on volume.
If you are supposed to make 35 sandwiches each with three slices of cheese, one slice of tomato, three pickle slices. You keep track by number of objects. You need 35 X 2 slices of bread per sandwich, 35 X 3 slices of cheese. No great deal of math here. Its simple.
The Unity glaze formula are organized in a similar manner; for each molecule of fluxes how many molecules of silica, alumina, and other oxides do you have?
Unity glazes formulae are standardized so that the number of mols of fluxes are always equal to one. That way you can easily compare the amount of flux to silica, or flux to alumina. Also it makes it easy to compare the distribution of fluxes from one recipe to another.
Here is the Recipe and Unity formula for Leach 1234 a common cone 10 recipe.
Leach 1234 Celadon Orton Cone 9-10
- Feldspar 40
- Limestone 30
- Silica 20
- Kaolin 10
The second column is the "R2O3? Column". It contains Al2O3? and B2O3?. B2O3? most often is included here but since it radically lowers melting point some people put it in the first column . Because it is also a glass former some people put it with Silica, the main glass former in glaze. While these are reasonable approaches I prefer it in the middle. It is most commonly put there and this makes comparisons easier.
One of the most useful and obvious parts of this format is the ability to look at the number of silica molecules in comparison to the fluxes. Any glaze with fewer than two molecules of silica per molecule of flux, at any temperature is unlikely to be very functional or stable in use. So long as the glaze is melted ,as this number goes up, the solubility seems to go down. Pure silica glass is very durable, hard, and insoluble.
Also the format allows one to see which flux dominates. In most stoneware glazes the light alkaline earths, calcium and magnesium dominate. They tend to make good functional glazes and are cheap. As magnesia goes up however the glazes tend to get more tendancy to crawl and tend more towards matts. With lots of magnesia, cobalt colors glazes more lavender and less blue.
Lithium, which is a very light metal, added to a glaze in just a few percent, often looks insignificant. A look at the unity formula tells you quickly that gram per gram lithium packs a lot of punch. In terms of numbers of molecules of fluxes 10 grams of lithium carbonate is the equivalent of ------- of Barium Carbonate.
The other big advantage of using Unity formula is that it allows you to more easily and accurately substitute ingredients. If you know the unity formula of a recipe using one feldspar for example you can easily substitute another and come reasonable close to the original glaze. Not using oxide formula for a glaze makes substitution a shot in the dark.