Decal definition

Have you ever wondered how did the custom-made design of bone porcelain produce? What’s the technology involved?

The main way to realize the custom-made design of bone China products, either it’s bone china mugs, or plates, or bowls, is decal technology. Decal, also known as water transfer decals, is a decorative process in which designs are first printed on a special paper pre-coated with water-soluble Glue, then soaked in water, and then transferred to the surface of bone China products. The decal paper consist of 3 layers, the bottom of the paper (also known as paper-based), the middle layer is Sol, and the surface of the cover oil.

The main production process of the decal paper for bone china products, you can refer to:Bone China Decal Paper Production Process

Decal classification

According to the production process, the decal paper production can be classified into three categories, which are on-glaze color, in-glaze color, and under-glaze color.

on-glaze decal

Bone porcelain that made of on-glaze technology is by directly applying the decal paper on the glazed surface, or paint directly on the surface of the bone porcelain, and then fired at 700-850 °C.

Because the firing temperature did not reach the melting temperature of the glaze layer, so the designs remain to stay at the surface and can not sink into the glaze layer,. If you touch with your hands and rub carefully, you will find that the surface of the product has a concave-convex sense, and you can observe uneven height with your eyes. On-glaze color is the main technical methods used in the massive bone porcelain production with its features of bright color, mature technology, easy to operate, and low price.

In-glaze

The firing temperature of the in-glaze technology is higher than that of the on-glaze, which reaches the melting temperature of the product glaze. The Ceramic Pigment sinks into the glaze when the glaze is melted and is covered by the glaze layer after cooling. If you touch the surface of the bone porcelain products, there is no obvious concave-convex feeling, its wear resistance is good, high surface brightness, high product grade, the cost is also relatively high.

The technology for the in-glaze decal is difficult, and the requirements for porcelain, kiln, and paper are strict. The test results of lead and cadmium can meet the requirements of the FDA and California Standard. This is a development direction of the ceramic field since people are paying more and more attention to the safety of the products.

Under-glaze technique

Under-glaze colored ceramics is a traditional decorative method in China.

All the colors of the products are decorated on the ceramic body and then glaze. After glazing, the products are fired once at a high temperature. Like the in-glaze technology, the surface is covered with the glaze layer, and the surface is bright and smooth, there is almost no sense of elevation. As a result of high firing temperature, the colors are easy to diffusion during the process, making it’s difficult to realize good decorative fine patterns effect, so the patterns used in under-glaze decoration, in general, are relatively simple.

With the color and pattern restrictions, under-glaze technology is unlikely to become the mainstream of the daily porcelain decoration method. Because of the features of high cost, the color is not abundant and the technical difficulty of in-glaze technology when comparing to on-glaze, the lead-free on-glaze decoration is the main development direction of ceramic decoration with no doubt.

What’s next

After the bone porcelain is decorated with the designs, it must be fired in the kiln at a certain temperature to make the designs permanently stay, this process is called decal firing. Different materials require different firing temperatures. After the appropriate temperature fired, the finished products are with bright colors, with patterns or designs stick to the porcelain surface, that’s not easy to scrape.

Classification of the decal by firing temperature

According to the firing temperature, the decal can be divided into high-temperature decal paper and low-temperature decal paper.

Low-temperature decal

The main component of low-temperature floral paper is ink material, when making pigment dry slowly, need enough time to fully dry to carry out the second process; low-temperature Floral paper firing temperature: at around 120-180 degrees. Low-temperature floral paper price affordable, bright color, versatility, gloss, three-dimensional sense of strong, anti-corrosion, and environmental protection, but weak adhesion.

The service life of low-temperature floral paper is shorter than high-temperature decal paper, the best applique time is used up within a month, too long then easy to oxidation, therefore it’s hard to keep stock for long use. The low-temperature technique is not applied to bone porcelain tableware.

High-temperature decal

High-temperature decal paper includes the three classifications we mentioned above, which are on-glaze color, in-glaze color, and underglaze color decals.

The on-glaze decal technique is mainly used for daily porcelain, its firing temperature is about 780 degrees, vary according to the color and materials of the decal surface. Gold-containing decal paper should be fired at a lower temperature. In-glaze and under-glaze colors are mainly used for artistic porcelain and daily porcelain that has very strict requirements for safety.

Why do we need to use a different temperature for firing

With firing temperatures ranging from 1,250 °C to 1,380 °C; high-temperature decal paper has good wear resistance and will not fall off even if it is placed for a long time, with strong adhesion, but its price is higher than that of low-temperature patterned paper, which is prone to go wrong during firing and with poor color performance.

Select the right temperature for firing the decal paper is particularly important. We need to choose different temperatures according to different colors n materials. In particular when the pattern is with gold, if the firing temperature is too high, it is easy to burn black, discoloration; too low, the color is not bright but dark. Furthermore, in the insider’s words, if the products are not fired sufficiently, the decal paper lead combustion is not sufficiently volatilized, leading to excessive lead content, which would have a bad influence on the health of the users in the long-term.

Conclusion

Once the decals are applied to the porcelain products, the products need to be thoroughly dried and then wiped with a dry cloth strip. After that product can be put into the kiln firing for around 4 times, and then the quality inspectors will select the qualified products and then pack in the boxes. Till then our production process will be over.

As easy it may sound like, there is much more knowledge involved in the producing of the custom-made bone porcelain, each step requires much experience. And besides the appearance, the safety of the products should be put in a more important position.

This principle not only applies to bone china tableware but also other daily ceramic tableware.
If you can’t be sure if the design is with microwave gold or not, refer to the instruction, otherwise, avoid putting the bone china tableware in the microwave might be a safer choice, what do you think?
Hope the above words helped you understand the is bone china microwave safe question. If you are interested in more bone china tableware knowledge, check the below links and share us your thoughts.

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