Decor firing – the final stage of porcelain refinement
The shaped porcelain body was smooth-fired into whiteware and the decoration was applied to this finished body in various processes. This decoration must now be thermally applied and consolidated in a further firing process so that it retains its stability and strength. Due to the low porosity of the porcelain, decors, as well as logos and vignettes, always have to be fired afterwards. This is the reason why decorative porcelain is always considerably more expensive than white porcelain. The type or position of the attachment of the decor is irrelevant.
Decor firing kilns
There are innumerable types and shapes of decorative furnaces, most of which are designed for the type and design of the common decorative variants of the respective factory. In the picture above you can see a circular kiln that is operated with electrical energy. This type of firing is relatively expensive, but the firing temperatures can be set very precisely and the decorative porcelain is protected against further condensation from gas residues . The start-up times (on-off) of such electric ovens are far superior to gas ovens. Such electric kilns are well suited for small runs, around up to 3,000 pieces depending on the type of decoration and firing temperature.
Most Asian chamber kilns (block kilns) are also suitable for producing decorative porcelain in a separate firing process. The capacities are higher than those of the circular furnaces, which are fired with gas. Due to the synergetic use of furnace and space, the Asian factories are more efficient and cheaper than the European porcelain factories in decor production.
Large quantities of equivalent decorative porcelain can also be fired in tunnel kilns . Here, too, it is usually fired with gas.
However, it is not the type and design of the kiln that is decisive for the decoration, but rather the firing temperature used and the firing curve .
Types of decoration according to firing temperature
Apart from the underglaze decorations , which are almost extinct today , the stability and longevity of every porcelain decoration depends exclusively on the firing temperature of the decoration firing. At Holst Porzellan, we differentiate between the following categories.
This process does not come from the porcelain industry and has nothing to do with “real decor firing”. Give-aways and advertising material porcelain is applied to the item by screen printing or direct printing and then briefly heated. The temperature range is mostly below 250 °C and thus cannot achieve any stability or strength. The decorative colors disappear quickly after repeated rinsing.
The economical firing method for porcelain decorations. The decor is traditionally fired between 750-900 °C (according to Friedl) . In our experience, however, the firing temperature of on-glaze decorations is between 640 and 850 °C using modern color compositions. The decorative colors are only applied to the glaze of the white porcelain and are thus “dishwasher-safe”. See our onglaze section for more information.
The inglaze process is the most common todayFiring method for decorative porcelain. The firing temperature of the inglaze firing is so high that the glaze of the white porcelain is heated to a viscous state, so that the decorative colors can sink into the glaze. Depending on the body and glaze, this takes place between 890 and 1,150 °C. Due to this high temperature, the choice of colors and gradients is very limited. Gold decorations, platinum rims and all other precious metals cannot be produced using the inglaze process. These metals would burn at the high temperatures. Inglaze decors are dishwasher-safe (dishwasher-certified) and also suitable for commercial use as hotel porcelain and catering crockery. The dishwasher resistance is more than 200 rinsing processes according to DIN.