•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
Ceramic inks are simply carriers of ceramic fine particled metallic oxide pigments (not raw colorants but prefired stain powders) that are used in automatic application techniques. Inks must have a physical consistency suitable for producing fine detail, this requires that they be suspended in a medium (as opposed to just water). Depending on the application technique, these mediums can be thick and flow like a printing ink. Or they can have a gel consistency that holds itself in place after application. Or they can be made from nano-size particled stains that stay in suspension in a highly fluid medium (for inkjet printing). They can be water or oil based. They may need to dry quickly, slowly and may not need to dry at all before firing. But the objective is the same: Tune a carrier for the application process so as to achieve a layer of metallic oxide based powder that will produce color exactly where desired and with crisp, well defined color edges.
Ceramic inks also need a melt carrier, that is, the metallic oxide colorant mix must be part of a larger silica:alumina:flux recipe that melts and envelopes it in a glass that will adhere to the body and be compatible with the over-lying glaze (or form a hard wear surface and be compatible with the under-lying glaze). The compatibility must also extend to matching the thermal expansion of the body and glaze and the melt carrier must also have a chemistry that is compatible with the color system. Each different stain system has its own needs and the melt carrier must be tuned to it. Carrier formulations even need to be adjusted with varying proportions of certain colors (to maintain the degree of gloss, for example).
Thus, formulating a good ceramic ink to work with the process at hand can be one of the most challenging task a technician will face. The simplest ink system is often used by potters: They mix glycerine with pure ceramic stains for rubber stamping. For some production methods and selected stain systems, this can be successful. The next level of complexity is to blend stains with a glaze base and suspend them in a colorless screen printing medium and then silk screen designs onto tissue paper, then transfer them onto the ware using water and pressure on the back side. It is now easy to print your own right or wrong-reading negatives on clear emulsion-treated acetates and photo-develop them onto a silk screen (youtube has many videos on the various techniques people are using). However in recent years, inkjet printing of ceramic stain based inks has all but taken over the entire ceramic world from hobbyist to the largest manufacturers. Many previously unrelated technologies have come together to make this possible. Inks have been highly tuned so they can be used in standard printers. The first major revolution was the ability to print decal transfers directly, this, combined with new software and other developments, brought unprecedented flexibility to the decoration stage of production. But now, specially designed printers spray the design directly on to the finished ware at high speed.
Compared to glazes these inks have very low density. Examples we have noted range from 1.02 to 1.3 (from two suppliers, demonstrating a range of tolerance within the inkjet system). Individual inks must be carefully maintained to density (as measured with hydro gravimeteic density instruments) and viscosity (e.g. Brookfield viscometer). Filtration testing and careful observation of printed tone are also part of the QC regimen.
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By Tony Hansen