What is glaze?
So first, you need to know what is glaze ? “glaze” is actually a kind of glassy thin layer attached to the ceramic body, as a necessary part of ceramic tableware. With regard to the origin of glaze, some scholars believe that it comes from the “ceramic clothes” used for decoration on pottery, that is, the coating applied by ancient pottery according to the characteristics of rough surface, easy water absorption and so on. With this layer or coating, to make the stoneware or porcelain waterproof, suitable for holding liquids. In addition, glazes can form a variety of surface finished, including glossy or matte finish, and also can do the decoration on the glaze, in glaze or underglaze.
1) Under glaze
Underglaze color is a major decoration technique of ceramics that appeared earlier. It’s to use pigment to draw various patterns on the formed and dried blank body (semi-finished product) and then cover with transparent glaze or light-colored glaze, final into the kiln with high temperature (1200-1400 ℃) firing. After firing, the pattern is covered by a transparent glaze film, and the surface is bright and soft, smooth, and translucent.
The characteristic of underglaze is that the color is well preserved and lasts for a long time. The color of the paint is well locked under the glaze, reducing the release of lead and cadmium and making ceramic tableware food safety.
In ancient times, underglaze is processed by handpainted, with the development of technology, most of the Chinese factory use transfer printing to decoration the ceramic in place with the handpainted. When this process is applied to ceramic tableware, the labor intensity and production cost can be greatly reduced, at the same time, the picture effect can be consistent, and it is convenient for mechanized flow operation.
The disadvantage of the printing process is that the color is simple, and only some regular and neat patterns can be printed. If the patterns are rich and complex, it is not suitable for the printing process.
2) In glaze
The in glaze process you can easily understand as to put a layer of light or transparent glaze on the porcelain body, burn-in low temperature around 800℃, and then paint on this layer glaze, final cover with a layer of glaze and burning at a high temperature 1050-1250 ℃.
The color in glaze does not belong to the category of ancient ceramic decoration techniquesbut is the title of a new porcelain decoration material and technique developed in the 1970s, also known as high-temperature fast-burning pigment.
Nowadays, most of the “in glazed” is mix with the pigment in the glaze, and firm it on the ceramic body directly. The pigment does not contain lead or cadmium, and it is applied on the glaze according to the on-glaze color method. Through the high temperature and fast firing of 1100-1260 ℃, the pigment infiltrates into the glaze and the glaze is closed after cooling. The products come out within glazed is not only delicate and translucent, rich in color, but also corrosion-resistant, wear-resistant, and no heavy metal dissolution.
3)On glazed
On the glaze process is necessary to make the white porcelain body first, then painting on the surface of the porcelain, and finally burn it in the kiln, so the painting and the glaze are burned separately.
Nowadays most of the on glaze process can understand as a decal, also known as ” moving flower”, it’s a decorative process which the design pattern is first printed on a special paper pre-coated with water-soluble glue, then soaked in water and then attached to the surface of the ceramic surface, final bake in the kiln with a temperature around 800℃. This is one of the most widely used decorative techniques in modern ceramics.
High-quality decal paper, the pattern is clear and delicate, color saturation, accurate color, no tortoise, no picture shortcomings, re-paste has ideal malleability, not easy to break, barbecue effect is ideal.
