The difference between ceramics (out of the misunderstanding of glazed and unglazed)

In our life, there will inevitably be porcelain and pottery. What's the difference between pottery and porcelain? This is an introduction for you.

First, the difference between ceramics

The difference between pottery and porcelain lies in: first, the use of materials; Second, the firing temperature is indispensable. Pottery can be made of various mineral clays, including porcelain clay. The firing temperature is relatively low, mostly between 700- 1000℃. The matrix is basically sintered and will not decompose when it meets water, but its porosity and water absorption are high. Observing the matrix under the microscope, there are few glass mullite crystals, in other words, there is no porcelain, and the tapping sound is dull. Porcelain is made of porcelain clay with high alumina content, that is, aged clay. The firing temperature of porcelain is at least above 1 100℃, and the embryo is basically porcelain. Microscopically, there are a large number of mullite crystals, with low porosity and water absorption and crisp knocking sound. Western scholars also regard the iron content in tire materials as the criterion for judging ceramics. They believe that fetal iron and other metal impurities are more and the color is darker. Porcelain tires contain less iron and are white in color. I don't think so. The amount of iron does not affect the nature of porcelain, but the aesthetic orientation is different. Take five famous kilns in Song Dynasty as examples. For example, Guan, Ge, Jun and Ding were all royal porcelains. Among them, the first four kinds are celadon products, and the iron content of the tire material exceeds the porcelain standard that westerners think. Only Ding Yao belongs to white porcelain, and the tire material has low iron content.

The difference between pottery and porcelain is not whether there is glaze or not. Pottery can have glaze, such as glazed pottery in the Han Dynasty (commonly known as Han Qing glaze) and colored glazed pottery in the Tang Dynasty (commonly known as Tang Sancai). Porcelain can also be unglazed, such as white porcelain. Because of its white and delicate texture, no one will regard it as pottery. In fact, the so-called hard pottery made of porcelain stone in southern China during the Shang, Zhou and Warring States periods has reached the level of porcelain, and the knocking sound is crisp and pleasant, which should also belong to the category of primitive porcelain.

Second, pottery

Pottery is an instrument made of clay or clay by kneading and firing. Pottery has a long history, and simple and rough pottery was first seen in the Neolithic Age. Pottery was used as daily necessities in ancient times [1]? Is it widely used as a handicraft now? Collection.

forming process

The most basic tool for potters is their hands. However, due to the long-term evolution of pottery manufacturing history, other additional tools have been developed, including pottery wheels and turntables, molding tools (clappers, mats and plasters), roller tools (roulette, clay tablets and rollers), cutting/hollowing tools (knives, slotting tools and wiring) and finishing tools (polished stones, wooden files and suede).

1, built manually or by hand.

This is the earliest, most personal and direct molding method. Pottery can be made of rolled clay, flat thick clay, solid spherical clay or a combination of the above three, and then made by hand. Some hand-made utensils are often made of mud or mud glaze (a mixture of soft water and clay). Handmade is a slower and gentler method than blank drawing, but it will give ceramists a higher degree of control over the size and shape of pottery. Although it is not difficult for experienced ceramists to make exactly the same handmade pottery, the speed and repeatability of rough drawing make it more suitable for accurately making a set of suitable items, such as tableware. Some ceramists think that hand-made art is helpful to create unique art by making full use of imagination, but others think that the spontaneity and directness of drawing ceramics are their inspiration.

2. Pottery wheel

Put the clay ball in the center of the turntable, which is called the wheel head. The Potter pushes (foot-operated billet puller or pedal wheel) or variable speed motor with a stick or foot. Usually, a plate made of rubber, wood or plaster of Paris is put on the grinding wheel head, which is called the blank bottom plate, and then the mud balls are thrown on the blank bottom plate instead of on the grinding wheel head, so that the finished product can be taken out together with the blank bottom plate without deforming it.

In the process of blank drawing, the pottery wheel will rotate at high speed, and the clay ball will be pressed, squeezed and slowly pulled out to become hollow. The first step is to press the rough clay ball downward and inward until it is perfectly rotationally symmetrical, which is the most important and difficult technique to master. Then "open" in turn, that is, punch a central hole in the mud ball; "Laying the bottom plate" means making a flat or round bottom in the container; "Throw" or "drag", that is, draw the shell closer and shape it into the same width; "Trim" or "flip", that is, remove excess clay to trim the shape or make a foot. ?

Although pottery wheels are usually used to make individual pottery, they can also be used for mass production. Making pottery wheels requires a certain skill of a ceramist, but a skilled mechanic can make almost the same plates, vases or bowls in one day's work. Due to the inherent limitations of the pottery wheel itself, it can only be used to make pottery that is radially symmetrical on the longitudinal axis. This situation can be made more interesting visually by stamping, unfolding, carving, making grooves, cutting surfaces, V-shaped cutting and other methods. Usually, the pottery made of drawing blanks will be further transformed by manual skills, adding functions such as handle, cover, foot and spout.

3. Spinning forming method

This method is carried out on the pottery wheel, which reduces the time needed to fix the shape of pottery. Overspray is a method to make the mold contact with the clay block still under construction on the gypsum mold. The spray tool shapes one side, while the plaster mold shapes the other side. Overspinning will only be used to make flat pottery, such as plates, but another technology, reverse spinning, will be used to make hollow pottery, such as cups. At least since18th century, full rotation and reverse rotation have been used to make pottery. Overspraying and backwashing are usually automated in large factories so that some semi-skilled workers can operate them.

4. Roller head blank spinning machine

This machine is used to mold pottery on a rotating plaster mold, such as over-rotation and counter-rotation, but there are rotating molding tools instead of fixed ones. This rotational moulding tool is a shallow cone with the same diameter and the same shape as one side of the finished product. In this way, relatively unskilled workers can make twelve pieces of pottery in one minute, which is related to the size of the finished product. Nowadays, it is very common to use roller spinning machines in factories all over the world.

5. Rolling and cutting machine

This is an industrial process of molding tableware and decorative utensils, by extruding a large amount of prepared clay into a space with the required shape composed of two piercing dies. After pressurization, compressed air will be injected from the perforated mold to release the molded pottery.

6. Dry pressing method

In this method, semi-dry granular clay is pressed into the mold. Porous die-casting mold with high-pressure water pump pumps clay into the mold. Clay, which becomes a granular substance, is made by spray drying, and its finished product is fine and flowing, with a water content of 5%-6%. This method is widely used in the manufacture of ceramic tiles, and the manufacture of optical discs is gradually transformed into this method.

7, grouting molding method

Casting slurry molding method is often used for batch production of ceramics, and it is also most suitable for pottery that cannot be molded by other methods. Mix water with green body to make mud glaze, and then pour it into gypsum mold with high water absorption. The moisture in the mud glaze is sucked into the mold, leaving a layer of blank to wrap the inner surface, forming an inner shape. Pour the excess mud glaze out of the mold, then open the mold and take out the contents. Grouting molding is very common in the manufacture of bathroom products, and it is also used to make small handicrafts, such as complex and exquisite statues.

Through the difference between pottery and porcelain and the introduction of pottery, it seems that pottery is more beautiful, but each has his own love. Which one do you like?

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