The so-called unsafe mainly refers to heavy metals that are easy to precipitate in porcelain dinnerware, such as lead and cadmium. If heavy metal elements accumulate in the human body, it may cause damage to the liver, kidney and immune system.
How to judge whether porcelain dinnerware is safe: In simple terms, it mainly depends on two points: the raw materials of ceramics and the firing of ceramics.
Safety of raw materials: those who use glaze colors should pay attention
The raw materials of ceramics include mud (green body raw material), glaze (glazed raw material) and paint (decorative raw material).
The raw material of the green body is generally kaolin or clay, which is basically safe because it is a natural clay or mineral without chemical addition.
So who is the bad guy? Glazes and Paints! Here, several concepts need to be explained first: on-glaze color, in-glaze color, and under-glaze color.
In a nutshell, color first, then glaze—creating with paint directly on the green or baked green body, then applying a layer of glaze, and finally firing it in the kiln. The prototype can be traced back to the Song Dynasty, mainly in blue and white, underglaze red and underglaze multicolored.
A layer of glaze is applied to the green body, then the surface is painted, and then another layer of glaze is applied. This is a decorative technique developed in the 1970s, mainly painting and decals.
The porcelain is first fired into a white glaze, then painted directly on the glaze, and then fired in a kiln. The second firing temperature is lower than the first firing. Porcelain made by this method is more suitable for display, because the color can be very bright, but sometimes it is not suitable for high temperature food. This is a coloring method created in the Ming Dynasty on the basis of underglaze blue and white painting, mainly ancient colors, pastels, new colors and enamel colors.
In most cases, the paints are low-cost chemical materials, which are likely to contain heavy metal elements such as lead and cadmium.
The underglaze and in-glaze colors have a layer of glass body (glaze) covering the paint, which also covers the possible heavy metal elements. In this way, it is clear at a glance which type of porcelain is the most dangerous: overglaze. Because its paint will be in direct contact with food, it is easy to release heavy metal elements at high temperature, causing harm to the human body.
How to burn it safely? high temperature!
To judge whether the ceramic tableware is safe, in addition to whether the paint is in direct contact with the food, it also depends on the firing temperature. Because in the process of high temperature calcination, the harmful substances disappear after chemical reaction.
The glaze is the glass body formed by the high temperature processing of the glaze, and the heavy metal elements will basically not remain after such high temperature treatment (about 1200 degrees Celsius).
And the color baking temperature of on-glaze color is only about 800 degrees, which cannot meet the above-mentioned "high temperature" conditions. In this case, whether it is safe or not depends on the quality of the paint. The better the quality, the lower the lead and cadmium content.
How to recognize glaze color at a glance
Having said that, you must especially want to know how to identify on-glaze, in-glaze and under-glaze colors.
The easiest way is to touch it directly. The outermost layer of the glaze color and the underglaze color is a layer of glass body, so it is smooth to the touch, while the on-glaze color is uneven.
If it is indeed glazed, you can soak it in vinegar to see if there is any visible fading or even paint peeling after a few hours. If there is, it is recommended to use less.
In general, high temperature porcelain is relatively safe. If there is paint decoration, then underglaze color is the safest. Overglaze porcelain is more suitable for decoration, or for cold food.
Porcelain of good quality generally leaves the decoration on the outside of the utensil, and the inner wall is left blank or decorated with high-temperature underglaze color. This will not only better reflect the true nature of the food, but also healthier.
Some porcelain is inherently a work of art and is only suitable for display, and it is best to be wary of cheap, brightly colored porcelain.
The quality of win-win ceramic tableware can be guaranteed through strict quality inspection.