3 Classification of Decal Production Processes

Have you ever wondered how custom-made design of bone porcelain are created? What are the techniques involved?

The main way to achieve a custom-made design for a bone china product, whether it is a bone china mug, a plate or a bowl, is the decal technique. Decal, also known as water transfer decals, is a decorative process in which the design is first printed on special paper pre-coated with a water-soluble glue, then soaked in water and transferred to the surface of the bone china product. The decal paper is made up of 3 layers, the bottom of the paper (also known as the paper base), the middle layer is Sol and the surface is covered with oil.

Decal classification

According to the production process, decal paper production can be divided into three main categories: on-glaze color, in-glaze color, and under-glaze color.

on-glaze decal

Bone porcelain made by the on-glaze technology is made by applying the decal paper directly to the glazed surface, or by painting the surface of the bone china directly, and then firing it at 700-850°C.

Because the firing temperature does not reach the melting temperature of the glaze layer, the pattern stays on the surface and cannot sink into the glaze layer. If you touch it with your hands and rub it carefully, you will find that the surface of the product is concave and convex, and you can observe the unevenness of the height with your eyes. With its bright colours, mature technology, ease of operation and low price, glazing is the main technical means of producing large blocks of bone china.

In-glaze

The inner glaze process is fired at a higher temperature than the glazing process to reach the melting temperature of the product glaze. The ceramic pigments sink into the glaze as it melts and are covered by the glaze when it cools. Touching the surface of bone china products, there is no obvious bumpiness, good wear resistance, high surface brightness, high grade products and higher costs.

The technology for the in-glaze decal is difficult, and the requirements for porcelain, kiln and paper are strict. The test results for lead and cadmium can meet the requirements of FDA and California standards. This is a development in the field of ceramics, as there is an increasing concern for the safety of the product.

Underglaze techniques

Underglaze porcelain is a traditional Chinese method of decoration.
All the colours of the product are decorated on the ceramic body, which is then glazed. After glazing, the product is fired once at a high temperature. As with the underglaze process, the surface is covered with a glaze and has a glossy, smooth surface with almost no façade. Due to the high firing temperature, the colours tend to spread during the process, making it difficult to achieve a good decorative fine pattern effect, so the patterns used for underglaze decoration are generally simple.

Restricted by the colour and pattern, the underglaze process is unlikely to become the mainstream of daily porcelain decoration methods. Due to the high cost compared to glaze, the lack of colour and the technical difficulty of the in-glaze process, lead-free glaze decoration is undoubtedly the main development direction for ceramic decoration.

What's next

After the bone porcelain has been decorated with a pattern, it must be fired in the kiln at a certain temperature so that the pattern is permanently retained, a process known as decal firing. Different materials require different firing temperatures. After firing at the right temperature, the finished product is brightly coloured, has a pattern or the pattern sticks to the porcelain surface and is not easily scratched.