Glaze absorption

Porcelain and ceramic crockery are always glazed - as far as general knowledge goes. It goes without saying that there are different qualities of glazes. However, one of the most important factors for the quality and finish of a glaze is not determined by the glaze itself, but by specialised knowledge. The definition and general explanation of ceramic glazes can be found on the main page of this section. What the layman commonly refers to as a "glaze defect" is in many cases not actually caused by the glaze itself, but merely manifests itself in a poor glaze appearance. The sources of defects lie below the glaze in the green body or in the material itself, e.g. in the binder of the granules.

One of the most important factors and quality-deciding criteria for the "true quality of a glaze" is the hardness, density and porosity of the green body! In factories that use the mono-firing process, these three criteria are replaced by the moisture content of the body. Regardless of whether mono or dual firing is used, a decisive factor for the quality of the glaze is the absorption efficiency of the green body.

There are two important factors that favour a high absorption efficiency of the ceramic body:

• high porosity
• a low moisture content

This reveals a shortcoming in industrial porcelain production: how do you dry a ceramic body without firing it? Drying chambers - of course! But with the production capacities of industrial porcelain production, their drying chambers would have to be the size of huge exhibition halls. So there is nothing left but biscuit firing.

At this point, we can certainly take up the cudgels for the mono-firing that is "so ostracised" in Germany. Sun-dried porcelain from Asian factories has the highest absorption efficiency for glazes. These are therefore applied much thicker than the glazes of highly sintered blanks in biscuit firing. This often means that the glazes from a good Asian factory are actually harder than those from European manufacturers. Another - extreme PRO - is the climate-neutral yield of solar energy, which - unlike biscuit firing - does not consume significant amounts of fossil fuels.