Pottery, Types, Procedures, and Techniques
Earthenware is porous pottery, usually fired at the lowest kiln temperatures (900°-1200° C/1652°-2192° F). Depending on the clay used, it turns a buff, red, brown, or black color when fired. To be made waterproof, it must be glazed. Nearly all ancient, medieval, Middle Eastern, and European painted ceramics are earthenware, as is a great deal of contemporary household dinnerware. Stoneware—water-resistant and much more durable—is fired at temperatures of 1200°-1280° C (2191°-2336° F). The clay turns white, buff, gray, or red and is glazed for aesthetic reasons. (Pottery fired at about 1200° C/2192° F is sometimes called middle-fire ware; its earthenware or stoneware traits vary from clay to clay.) Stoneware was made by the Chinese in antiquity and became known in northern Europe after the Renaissance (14th century to 17th century). Porcelain is made from kaolin, a clay formed from decomposed granite. Kaolin is a white primary clay—that is, a clay found in the earth in the place where it was formed and not transported there by rivers; secondary clays, borne by rivers to the site of deposit, contain impurities that give them various colors. Porcelain is fired at 1280°-1400° C (2336°-2552° F); it is white and often translucent. Porcelaneous ware was first made in China, hence its common name china. Chinese porcelain is less vitrified (and therefore softer) than its modern European counterpart, which was developed in Germany in the early 18th century. European imitations of Chinese porcelain are also made; called soft-paste or frit porcelains, they are fired at about 1100° C (about 2012° F). In the mid-18th century, English potters invented bone china, a somewhat harder ware that gained whiteness, translucency, and stability through the inclusion of calcium phosphate in the form of calcined (fired, chemically altered) ox bones.
A. Preparing and Shaping the Clay Continue reading
Types of Pottery
Ceramics
Originally from the Greek keramos meaning pottery.
Of or relating to the manufacture of, or any product such as earthenware, porcelain, or brick, made essentially from a nonmetallic mineral such as clay, by firing at a high temperature.
Clay
Clay is the basic material of pottery and has two distinct characteristics – it can be moulded and it hardens on firing to form a brittle but otherwise virtually indestructible material that is not harmed by any of the corrosive agents that attack metals or organic materials.
Pottery
Pottery is made of clay and is permanently hardened by firing in a kiln. The nature and type of pottery is determined by the composition of the clay and the way it is prepared, the temperature at which it is fired, and the glaze used. There are three basic types of pottery; Earthenware, Stoneware and Porcelain.
Earthenware
Earthenware was the first kind of pottery made, dating back about 9,000 years. In the 20th century, it is still widely used. It is pottery that has not been fired to the point of vitrification and is thus slightly porous and coarser than stoneware and porcelain. It is made waterproof by the application of a tin or clear glaze. Nearly all ancient, Continue reading
Body Calculations
Body Mixing
In the manufacture of all ceramic products the requisite quantities of components (flint, stone, ball clay, china clay, bone, etc.), are measured in terms of weight or volume then subjected to a mixing process.
For most ceramic bodies, the actual mixing takes place in slips form, which ensures an intimate blending of the constituents and hence a uniform product. The original quantity of each component may, however, be measured out in the dry state or in slip form.
“Dry” Measurement
The component powder materials are simply weighed out then transferred to the mixing ark-due allowance being made for any moisture content
An older technique, sometimes used in the manufacture of bone
china, is to fill and level-off a “standard box” with the dry powder component. A specified number of boxes of each material is then used in the body mix. This of course, is an attempt to measure the dry materials on a volume basis. It suffers from errors due to inconsistent packing, and variable moisture contents of the raw materials.
“Wet” Measurement
The most widely used method, in British practice, is to obtain a stock of each Continue reading
Cara mengatasi masalah Glasir
Glaze troubleshooting
Di Industri keramik, masalah mesti akan muncul karena beberapa sebab, yang utama karena pemakaian bahan baku yang tidak stabil. Bahan dari alam mempunyai beberapa lapisan, dengan kadar misalnya Silika yang berbeda-beda. Untuk memperkecil masalah tersebut biasanya pemasok bahan keramik yang besar, mengolah bahan tersebut dihancurkan sehingga berbentuk kecil atau kadang bubuk, kemudian digiling didalam mesin penggiling sehingga keluar berbentuk noodle ( mie besar )
Masalah yang umum dan kebanyakan adalah sebagai berikut:
Pinhole
Barangkali yang paling sering terjadi pada Glasir, adalah Pinhole (lubang jarum). Terdapat lubang kecil diatas permukaan Glasir yang menembus sampai permukaan Clay Body/ keramik. Ini disebabkan adanya gas-gas yang lepas dari dalam bahan keramik selama pembakaran (firing), didalam Clay Body/ Barang Keramik terdapat bahan-bahan ( karung plastik bekas bahan, kayu, akar tanaman dll ) yang kecil yang mudah terbakar pada temperatur yang Continue reading
RAW MATERIALS
RAW MATERIALS
RAW CLAYS
The theoretical formula for clay is Al2O3 2SiO2 2H2O, an alumina-silicate, but none are that pure and uncontaminated. There are many technical characteristics that define a material as a clay but, for ceramics, the primary characteristic beyond the alumina and silica content is the fact that they are composed of very small flat platelids with a resulting very large surface area with microscopic water between them so they slide on one another and additionally tend to hold their shape. Additional properties of clays are 1) harden when dried and become permanent when fired, 2) shrink during drying and firing, 3) refractory (resist softening at high temperature), 4) heat, sound and electrical insulation. Continue reading
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