Is there a small black spot on the purple sand cup?

The purple sand mine produced in Yixing belongs to silty sedimentary rock, and its main components are silicon, iron and aluminum. These three components in purple sand are enough to form compounds such as time, kaolin, hematite and mica.

Sometimes we will see some small black spots, small stars and small white spots on the pot. In fact, this is all normal. I don't want to tell an anecdote before explaining the reasons for the formation of these points. For a time, pot players in Taiwan Province Province didn't know much about the foundation of purple sand. I even use my unique vision to measure the quality of a teapot by the standards of industrial finished products. Looking at a teapot by this industry standard, "small black spots", "small star spots" and "small white spots" naturally become the "big shortcomings" of the teapot. In order to overcome these "shortcomings" on the surface of teapot, teapot is more suitable for the taste of consumers who measure the quality of teapot from the industrial point of view. The mud refiner invented a method of making mud, which is called "mud washing and sand washing". Mud-sand washing method refers to the high-density crushing of mineral raw materials containing a small amount of impurities, which should be carefully selected, so that the diameter of impurity particles becomes smaller and it is difficult to see with the naked eye after firing. In this way, the purity of mud has not been improved in essence, but there are no "spots" on the surface, which makes it look more "beautiful", maximizes the use of mud resources, reduces the cost and makes it. Will purple sand mud lose its "sand feeling" when it hits the pot? After thinking, I think this "mud washing method" is really not desirable. On the other hand, the traditional "artificial system" or "normal mechanism" often requires much more than the "mud sand washing method" standard, so that all optional impurities can be removed to the maximum extent in the selection of mineral materials, and the cost will naturally increase. Let me ask you, are some pots with small stars, small black spots and small white spots produced by "manual grinding" or "normal mechanism", or are the pots produced by "mud washing and sand washing" with many impurities but invisible?

Let's go back to the cause of the dot. It can be seen from the composition of purple mud above that the real purple mud must contain mica. Mica looks like a blinking dot on the burned pot surface, which is what I said above.

1, mica < r+R23+[alsi3o10] (oh) 2.

> It is a mixture, belonging to aluminosilicate minerals and layered silicate, and it is a composite silica layer composed of two silica tetrahedrons and an alumina octahedron. Because the hardness of mica is not high, it can be dissolved with other mineral materials when it reaches the melting temperature of mica to strengthen the connection between mud bodies. The structure of mica is destroyed at 1050℃, but it will not volatilize, and the vaporization temperature of the contained substances is much higher. The optimum firing temperature of Yixing purple sand is between 1 100-1280 (depending on the mud), so it is normal for mica to remain on the surface of the pot.

2,

Occasionally, there are small black spots on the pot body, which are polymeric insolubles of metal compounds such as iron or manganese. Friends who went to middle school all know that iron oxide (Fe2O3) is oxidized into ferroferric oxide (Fe3O4) after calcination, which is magnetic and black in color. This is the "little black dot" I mentioned above.

3,

In addition, because sedimentary rocks often contain fossils, fossils mainly composed of calcium carbonate (CaCO3) turn into hydrated lime during high-temperature firing, forming "small white spots" on the surface of the pot. When brewing, it absorbs water and expands, and then falls off. The so-called "ash explosion" (that is, the defect point on the surface of the teapot) was produced. These are very common phenomena in mud, and they are also a small weakness of purple sand mud itself.

There are no features such as "small star spots", "small black spots" and "small white spots", which shows that this raw material is not made by hand grinding or normal mechanism, but is replaced by "mud sand washing" or other mineral sources with less mica content (maybe not purple sand ore), which is a kind of artificial deliberate destruction of the natural beauty of natural materials. An old pot friend told me that I am not interested in a teapot without a "little star". Hehe, everyone knows the reason after the above.