Understanding ceramic and glass decorating - Techniques

When printing directly onto glass and ceramics, screen printing and pad printing can be used. There is a combination of both processes called “Total Transfer.”

This is where the image is screen printed onto a flat plate and then picked off by a silicone pad and transferred to the article. The decorated product is then fired in the normal way. 

The reason for using this process is to enable relatively thick deposits of ink to be printed with the pad-printing process, as shown in the picture below.

Image courtesy of PDS International Limited

Pad Printing with Thermoplastic Inks

Pad printing with heated plates and thermoplastic inks works very well but there are pros and cons for both systems. Four colour process is possible with inorganic Cyan, Magenta, Process Yellow and Process Black.

This is not for the inexperienced as colours can easily change in the printing and firing process. You don’t have the benefit of colour bars, greyscales or density measurement as the printed colours change during the firing process and you can’t guillotine off the colour bars.

The simpler alternative to direct printing with ceramic colour is to produce waterslide or heat applied transfers. These transfers are produced by screen printing and lithographic printing. Waterslide use water soluble glue that allows the image to lift off special paper before being positioned on the substrate.

Heat applied transfers come off the carrier paper or film when applied with a heated blanket to the substrate. In both cases the applied image has to be fired at elevated temperatures. 

Sublimation

None of these methods should be confused with sublimation transfers that appear to print onto ceramics and glass but are in fact producing an image in a polyester lacquer that has been sprayed or dip coated on to the surface.

Although very attractive this is not as resistant as fired enamels or even UV cured inks. Sublimation inks are not particularly colour safe in sunlight or elevated temperatures but it is still a big market particularly in personalisation and business gifts.

Developments in the dyes and application methods are increasing the use of the process which is ideally suited for the use of digital printing in the creation of the transfers.

In summary the options are:

• Inorganic ink that can be screen printed or pad printed but requires a kiln or lehr to fuse the enamel to the surface.
• Organic ink that can be screen printed or pad printed that requires heat or Ultra Violet energy to cure. If the curing methods is heat then the maximum temperature will be in the region of 180^oC for a period of time.
• Waterslide or heat applied transfers printed with inorganic ink that have to be fired in a kiln or lehr.
• Sublimation systems are an ideal means of decorating a huge range of polyester objects and substrates.

Production of Transfers

If you don’t have the kiln or lehr, as a screen printer, the production of transfers can still  be a very good business. There are still some very able printing companies making an excellent living from this market.

Four colour process printing provides great results particularly as the firing process in the kiln helps blend the colours and reduces the characteristic dot patterns.