|Monthly Tech-Tip |
You can make your own ink (or buy it) and apply it to ware using various methods (e.g. rubber stamping, silk screen, inkjet decals).
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.
Ink Jet Printing
Ink jet printed decoration is now pervasive in all parts of the ceramic industry. And in hobby also.
Silk screen printing
Silk screen printing is one of the best options for hobbyists and potters to reproduce crisp and detailed decoration for their ware. But there are many details to know.
This process of printing a design (using ceramic inks) onto film-coated paper to create a waterslide transfer. On wetting, the film decal can slide off the backing on to the glazed ware.
Inkjet Decoration of Ceramic Tiles
Theory and description of various ceramic ink and inkjet printing technologies for ceramic tile, the issues technicians and factories face, inket printer product overview.