Monthly Tech-Tip | No tracking! No ads! |
This specific problem is happening after some years of use.
A glaze may look smooth visually, but is it really? If the surface has micro-cavities and surface disruptions this could give organics a place to attach and build up. Firing curves need to take into account the LOI of glaze materials (which can affect the microsurface) like calcium and barium carbonate, dolomite, talc and even clay.
Has the mirco-surface of the glaze changed? Many labs offer surface analysis services so it is possible to have a surface compared with one known to be good.
Is the glaze subject to leaching? This could happen if the fired matrix has excessive phase changes, possibly due to poor mixing, frit quality issues or materials of excessive particle size (e.g. use 400 mesh silica instead of 200 or 300). A change in the flow of a routine melt fluidity test can alert you to changes in materials or slurry preparation.
What grade of zircon do you use? It should be 5 micron. Are you using high-energy mixing to separate the zircon agglomerates? Zircon is implicated in cutlery marking, if your glaze is marking this puts suspicion on the zircon as at least part of the problem.
Is your glaze fired at the temperature to produce optimum hardness and durability? Firing it higher and lower than the production temperature and test surface properties. If you determine, for example, that it is under-firing, then add flux to melt it a little more. If it is under-fired, add SiO2 or Al2O3 or reduce flux (KNaO, MgO or CaO).
Troubles |
Staining of Fired Ceramic Glazes
Ceramic glazes are glass. That means they are always easy to clean, right? Wrong. If the surface is not developed it will be difficult or impossible to clean. |
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Glossary |
Sanitary ware
A type of porcelain zircon-glazed ceramic that includes bathtubs, sinks, toilets, etc. |
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