Percent Analysis
Each raw material in ceramics, like Potash Feldspar or Kaolin, has its own chemical composition. This is represented by percentages of different oxides (such as SiO2, Al2O3, etc.) that the material contains. These analyses tell us about the material's properties, like how it will melt, harden, or react with other ingredients.
Example Percent Analysis:
| Material | SiO2 | Al2O3 | K2O | CaO | LOI |
|---|---|---|---|---|---|
| Potash Feldspar | 64.8% | 18.3% | 17% | - | 0% |
| Silica | 100% | - | - | - | 0% |
| Whiting | - | - | - | 56.1% | 43.9% |
| Kaolin | 47.3% | 40.2 | - | - | 12.5% |
LOI
Loss on Ignition (LOI) refers to the percentage of weight a material loses when it is heated to a high temperature and any volatile substances are burned off. In ceramics, this measurement helps to understand the presence of substances like water or carbonates in a material, which can affect the final properties of the glaze or clay body.
When materials are combined in a recipe, each material contributes oxides to the recipe's total percentage analysis. So if Potash Feldspar, which contains a certain percentage of K2O (Potassium Oxide), makes up 40% of a glaze, then 40% of that K2O is contributed to the total glaze's K2O content. Adding up these contributions from all materials results in a total percentage analysis, giving a full picture of the glaze's chemical composition.
Example of a glaze recipe with 40% Feldspar, 30% Silica, 20% Whiting, and 10% Kaolin:
| Material | Amount | SiO2 | Al2O3 | K2O | CaO | LOI |
|---|---|---|---|---|---|---|
| Potash Feldspar | 40% | 25.9% | 7.3% | 6.8% | - | 0% |
| Silica | 30% | 30% | - | - | - | 0% |
| Whiting | 20% | - | - | - | 11.2% | 8.8% |
| Kaolin | 10% | 4.73% | 4.02% | - | - | 1.25% |
| Total | 100% | 60.63% | 11.32% | 6.8% | 11.2% | 10.05% |
In this example, Silica is 30% of the recipe. Since Silica consists of 100% SiO2, Silica contributes 30% SiO2 to the final recipe.
Glaze percent analysis in ceramics provides a detailed understanding of a glaze's composition, revealing the percentages of different chemical compounds like silica, alumina, and various fluxes. This analysis is vital for predicting the glaze's properties, such as hardness, melting temperature, texture, and glossiness. By knowing these percentages, ceramicists can reproduce or modify glazes consistently, much like tweaking a food recipe. Essentially, glaze percent analysis blends science and creativity, allowing precise control over the appearance and functionality of the ceramic piece, and helps in understanding, controlling, and experimenting with the complex chemistry of glazes.