The so-called “glaze” is simply a colorless or colored vitreous thin layer covering the surface of ceramic products.
What are the differences between overglaze, underglaze and underglaze colors?
1. Overglaze color:
The on-glaze color is first fired into a white porcelain body, then created with pigments on the surface of the porcelain, and finally fired in a kiln.
The on-glaze color is first fired at a kiln fire of about 1200°C to 1300°C into a white porcelain blank, and after drawing the pattern with pigments, the second kiln firing is performed at 800°C.
Porcelain made in this way has hundreds of pigment colors, which are extremely expressive. The final firing temperature of the pigment is very low, and the color changes little after firing. The pigment is not fused with the glaze, so the drawn patterns stand out from the glaze surface, which is easy to fall off and change color after long-term friction and erosion. Because the pigments on the glaze contain heavy metals that are harmful to human health, such as lead and cadmium. Therefore, if it is found that there is a phenomenon of falling off, it is best not to use it.
Lead is a poison that acts on various systems and organs of the body, and the toxicity is accompanied by lifelong, not to mention children, and can lead to lifelong disability in severe cases.
Cadmium, mainly used in coatings, electroplating and plastic stabilizers, will accumulate in the kidneys after entering the human body, and eventually cause uremia. Cadmium ranks 7th among the 275 most toxic environmental poisons in the US Centers for Disease Control and Prevention.
If on-glazed dinnerware is used to hold food, lead and cadmium will be easily dissolved out and brought into the body, causing chronic poisoning that is not easy to find; and if it is low-quality on-glazed porcelain with many colors, it will be made into dinnerware , it is likely to cause acute heavy metal poisoning.
2. Color in the glaze:
In-glaze color is painted on already glazed porcelain, and after the painting is completed, it is covered with a layer of glaze, and then fired at high temperature.
In-glaze color is to make the glazed green body first bisque fired at 800°C, then painted, and then spray a thin layer of glaze on the surface, and then quickly fired at 1060-1250°C for 90-100 minute.
Under the condition of high temperature and fast firing, the glaze of the product softens and melts, so that the particles of this new pigment penetrate into the glaze. Has an underglaze effect. This kind of decoration with high-temperature fast-burning pigment has a unique style, its color is soft and smooth, the product has strong mechanical wear resistance and corrosion resistance, and at the same time completely solves the harm of “lead poisoning” in ceramics.
3. Underglaze color:
Underglaze color is created directly with pigments on green or baked china, then glazed, and finally fired in a kiln. The pigments can fully penetrate into the porcelain.
Underglaze color is created directly on the green body. It only needs to be painted with pigments, then glazed, and then fired in a kiln at about 1200°C to 1300°C. Or to paint underglaze painting on the china, first fire the clay at 800°C into the china, and after painting and glaze, it will be fired in a kiln at about 1200°C to 1300°C.
The painting method is to use pigments for color painting decoration first, and then apply glaze on it, and the glaze is on the outermost layer. Therefore, the color of the utensils painted under the glaze is smooth, the surface is smooth, the penetration is continuous, and the color will never fade. It is very safe as daily use porcelain (such as cups, bowls, scoops, pots, etc.).
It can be seen that the painted surfaces of underglaze and underglaze colors are safe because they are separated by enamel and do not come into direct contact with food. On the other hand, the painted surface of the glaze color is in direct contact with the food. In addition to being unhealthy, it is more likely to precipitate when exposed to acid.
How to choose ceramic dinnerware?
1. It is best to choose pure white ceramic dinnerware. Because they are not painted, do not use pigments, and do not contain heavy metals that are harmful to the human body.
2. If you like ceramic dinnerware with patterns and patterns, it is better to choose underglaze color or underglaze color, which is safer. Don’t choose glazed ones. The bottom of the ceramic dinnerware or the product label will generally indicate: underglaze color, underglaze color or overglaze color, pay attention to identification when purchasing.
3. Try not to choose ceramic dinnerware with metal decoration, such as gold-rimmed bowls, gold-rimmed plates, gold-rimmed cups, etc., because manufacturers will not use real gold for consumers, and these gold colors are also heavy metal paints.
Finally, the glazed surface of ceramics should be avoided to be wiped with rough objects.
Post time: Jun-28-2022