Frit

Alternate Names: Ceramic Frits

Description: Frit master

Notes

Frits are made by melting mixes of raw materials in special kilns, then pouring the molten mix into water and finally grinding it into a fine powder. Frit suppliers refer to the use of their frits in 'partially fritted' and 'all-fritted' glazes. The latter generally refers to glazes with 90% or more frit, the former to 90%.

Although the fritting process is expensive there are many advantages to using frits in glazes, enamels, etc. The frit topic in the glossary section itemizes the many reasons why frits are so useful. Many things that are impossible with raw materials can be done with frits (the converse can also be true), demonstrating that we must consider more than just chemistry when evaluating why glazes fire the way they do.

The Frit market is driven by large customers (especially tile) who use recipes given to them by the prepared glaze industry, the engineers at these companies work at the recipe level and often do not even know all the details of the chemistry of the frits they use. The availability of smaller quantities of frits is generally determined by what industry is using. The frit market changes with time. Frit companies make many more products than what their literature or websites display, these are legacy formulations or custom mixes.

Some frit companies provide the chemistry of their products, others did in the past but do not do so now. Some provide approximate analyses. In the eyes of someone interested in the chemistry of the glazes they make, this practice or non-disclosure partially defeats a key purpose of using frits, namely, having control of chemistry. In fact, the lack of chemistry is a key disadvantage of using certain brand names. For example, the frit manufacturer might recommend substituting part of one frit for another in a recipe to solve a specific problem (like crazing). The problem with this is that the new frit might have a chemistry that is hostile to the pigments being used, the degree of gloss, the hardness, resistance to devritification, etc. Without the chemistry, the new frit can be a bit of a pandora's box. The lack of frit chemistry information works against the general trend of using ceramic calculations to take control of glaze properties. Another factor is the general ignorance of how to use ceramic chemistry software to manipulate recipes to target or maintain a specific chemistry. But this is changing and we are sure that pressure will come to bear on manufacturers as expertise improves.

Admittedly, each manufacturer makes specialized frits (i.e. strontium, lithium compounds) that they invest heavily in R&D to develop. Keeping the makeup of these a secret protects against the formulations being copied by other manufacturers. Even though powdered samples of these frits could be analyzed by competitors to deduce their approximate makeup, the tightly controlled chemistry required to achieve the intended effect may not be competely evident. Thus the actual production of a duplicate can be a more elusive goal than it at first seems.

One other factor to consider is the old principle: 'You get what you pay for'. Two frits may appear equal, being pure white powders having a given chemistry. Like any other industry, some companies, especially in developing countries, take shortcuts that affect their adherence to the stated chemistry, the homogeneity of the mix, solubility, particle size or the presence of impurities and unmelted particles.

BaO, SrO, Li₂O, ZnO special purpose frits are commonly used in industry (in middle and low-temperature glazes) however potters focus on glazes that employ only the typical KNaO, CaO and MgO. This is because they find the raw materials that source the former are either toxic, troublesome to use or cause firing faults. While they are more expensive than typical boron frits, using them you can produce glazes with better fit, melting, surface, brightness, color, clarity and with fewer firing faults.