Friends who come into contact with Jianshui purple pottery often find that there are some white substances left in the mouth of purple pottery pot and purple pottery pot, especially in the large purple pottery jar cover. What is this white substance? Is it harmful to your health?
This white substance, called alumina, is an oxide. It is characterized by high temperature resistance and its melting point can reach 2054 ℃.
In the process of firing Jianshui purple pottery, alumina is used to prevent the lid from sticking together due to high temperature, and to prevent the bottom of the purple pottery and the shed board from sticking together.
When firing purple pottery, in order to achieve the same proportion of shrinkage, it is easier to operate in the later stage of the whole mouth. The lid and body of the pot, the lid and the body will be buckled together and fired at the same time. In the high temperature of more than 1100 ℃, the cover and the body are easy to stick together, resulting in failure to open. At this time, it is necessary to brush a layer of refractory and anti adhesion agent in front of the cover, which is alumina.
In the same way, a layer of alumina anti sticking agent should be sprayed on the surface of one layer of shed board to prevent the ceramic body from sticking to the shed plate during high temperature firing.
The special point of purple pottery is that it still needs to be trimmed and polished after being fired. After these two processes, most of the alumina will be ground off, but some will still remain at the cover opening. Is this residual alumina harmful to health?
Alumina is a kind of ubiquitous substance. Aluminum will react naturally after contacting with oxygen. In our daily life, we often cook vegetables in aluminum pots and water in aluminum pots. As time goes on, the surface will naturally oxidize to form a layer of alumina film. Its function is to protect the aluminum pot from further oxidation.
Our daily meals are generally exposed to alumina. The actual research results also show that alumina has little impact on human health, and its circulation is not subject to any national restrictions. Therefore, if you find white alumina on the lid of the purple pottery jar, you don’t have to worry about it. You can use it at ease.