Ceramic glaze slurries can sometimes generate enough foam that it becomes difficult to apply an even layer to a surface. What can you do?
Some ceramic glaze suspensions will foam as they are mixed and used. This is problematic since the bubbles prevent the laydown of an even surface. The reason for the foaming relates to issues with particle agglomerations, surface tension and incompletely wetted particle surfaces hanging on to air bubbles.
Glazes containing spodumene or calcined kaolin, for example, can have this problem. Or glazes containing materials having surface treated particles (e.g. colorants that are normally unstable like red copper oxide). A possible solution is power-mixing a slurry to input enough energy to wet all particle surfaces. Or mixing the slurry using hot water. A more drastic solution, practical for potters, is washing the offending material (by slurrying it in plenty of water, settling it, pouring off the water and drying it out, e.g. for spodumene). Another option is to substitute the offending material for another less troublesome one that can supply the same oxides, glaze chemistry is normally needed to be able to do this (a common example is the use of a frit to supply an oxide, like lithium, rather than a raw material like spodumene).
Foaming glazes can be a problem in industry and surfactants (defoaming additives) are commonly available and industrial technicians know how to use them. Some of these agents are just common household products (see the Wikipedia link below).
Defoaming agents at Wikipedia
Surfactants at Wikipedia
Defoamers on Wikipedia
In ceramics, glazes are slurries. They consist of water and undissolved powders kept in suspension by clay particles. You have much more control over the properties than you might think.
Ceramic Glaze Defects
|By Tony Hansen
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