|
Ceramics is a field with two major categories: Pottery and Porcelain. Pottery was the first entirely man made objects produced by primitive societies. The basic materials and the techniques used remained unchanged for thousands of years. A major development occurred during the 7th century AD in China, where with the discovery of kaolin and the method of creating hard paste porcelain, the field of ceramics started a new age.
The following information should provide the basics for the evaluation of modern European porcelain. Essential factors in the assessment of value: Body The body is the materials in which a piece is made of. The distinctions between these types of ceramics stem from the use of different material, the temperature at which the piece is fired in the kiln, and the proportion of vitreous (glassy) ingredients in the body. Important test is to hold the article up to a strong light. If light shows through the body of the piece, it is either porcelain or thinly potted stoneware. If the body does not transmit light, it is earthenware. This is a reliable rule of thumb. Stoneware is generally unglazed, or glazed with vaporized salt which creates a characteristically rippled surface. Important consideration in valuing a piece, is the amount and quality of hand work involved in the creation of the body. Was it casted by machine, casted as a single unit, formed by a pattern or was it hand made? Hand piercing, intricate decorations such as flowers adds to the value of the piece. Pottery Pottery is of much coarser texture than porcelain. The two main types of pottery are porous earthenware and non-porous stoneware. Earthenware: Below 2200 F (1200 C) is the “low” temperature range, wares fired within this range are categorized as earthenware. Most common clays are suitable for earthenware, and the resultant body may be white, buff, brown, red or gray depending not only on the natural color of the clay but also on its iron content. Stoneware: Made from clays that allow shapes to retain their form at temperatures up to 2250 F (1400 C). In this “high” temperature range the clay “melts” and fuses into a non-porous vitrified body of great strength. These vitrified bodies can be slightly translucent, are impervious to liquids and are extremely hard and durable. As with earthenware, the resultant bodies can vary in color. Stoneware bodies were made in Europe, predominantly in Germany, from at least as early as the 15th century. Porcelain Porcelain is a fine variety of ceramics that was first made in China in the 9th century AD and widely imitated in the West till the 18th century. Overglaze decoration on hard-paste stands out distinctly, on soft-paste the decoration tends to sink into the glaze. The distinction between the two pastes is especially obvious on figures. The close-fitting glaze on hard-paste enables crisper, more detailed modeling, whereas soft-paste figures have blunter outlines, often with glaze pooling in the crevices. Hard-paste porcelain: Hard-paste porcelain contains two essential elements - kaolin (china clay) and petuntse (china stone). Both are forms of decomposed granite. They are fused together by firing in a kiln. First the object is fired to about 1650 F (900 C), then dipped in glaze, then refired at about 2400 F (1300 C). The china stone bonds the clay particles together and gives translucency: the high temperature gives object the consistency of glass (vitrifies it). Chips on hard-paste porcelain appear smooth and glassy. In Europe a source of kaolin was find and porcelain manufacture was attempted at Meissen, near Dresden. By 1718 petuntse had been located, and so began the production of the hard paste white porcelain for which Meissen became famed. Soft-paste porcelain: Soft-paste porcelain was first made in Florence, Italy, in ca. 1575. As its name suggests, soft-paste is more easily scratched than hard-paste. The glaze sits on the surface of the ware, feels warmer and softer to the touch, and is less glittering in appearance. Chips in soft-paste have a floury appearance like fine-grained chalk. Kinds of soft-paste: Several soft-paste formulas were discovered, each using fine clay but adding different ingredients to provide the all-important translucency. Frit porcelain: Using powdered glass made from a combination of substances including white sand and gypsum. Soapstone porcelain: Using powdered soapstone. This yielded a white, more plastic body. Bone-ash porcelain: Using powdered calcined ox-bones. This body was denser, generally more thickly potted, and heavier. Bone china: This characteristically English porcelain, invented c. 1794, is nearer to hard- paste than soft-paste. It made use of a large proportion of bone-ash added to hard-paste ingredients. Feldspar china: This was a type of English porcelain in which feldspar replaced china stone in the bone-china formula. Biscuit: Biscuit is a term applied to a stage in the production of pottery or porcelain after it has been fired once and not glazed. It is specifically applied to porcelain figures sold in an unglazed state, Characterized by their matte, porous surface. They were made from the mid -18th century by Continental factories and in England by Derby from 1773. Glaze The purpose of a glaze applied to a piece of pottery or porcelain is to make it waterproof, or enhance the brilliance of the color. Glazes can be translucent, opaque, or colored. Hard-paste porcelain was given a feldspar glaze similar in composition to the body itself. When fired, the body and glaze fused together. The principal pottery glazes are: Lead glaze: A transparent, glassy tight-fitting glaze used on most English and Continental soft-paste porcelain, and on earthenware such as creamware. The lead in early lead glazes tended to absorb into acidic liquids, such as vinegar, making them poisonous. Tin glaze: A glaze to which tin oxide has been added, giving an opaque white finish. This is a very important and broad group of wares, divided into different categories according to country: Maiolica: (Renaissance Italy) Faience: (17th century France and Germany) Delft: (17th and 18th century Netherlands) Delfware: (17th and 18th century England) Majolica - a type of 19th century earthenware decorated with colored glazes. Salt glaze: A glaze formed by throwing common salt into a kiln at about 1800 F (1000 C) during the firing of stoneware. The sodium in the salt combined with silicates in the body to form a thin, glassy glaze. Colored glazes: Used on earthenware from the mid - 18th century England. They are also found on Chinese pottery and porcelain: these are mainly derived from oxides of iron. Crazing, firecracks and pinholes: Crazing: is a network pattern that appears when a lead glaze “warps”. It is a feature that occurs in pottery and some early soft-paste. It is not found on hard-paste. Firecracks: are sometimes formed in soft-paste during firing in the kiln. Pinholes: are minute air bubbles. Decorations Underglaze Overglaze Colored glazes Hand painting or transfer printing Gilding Underglaze: In underglaze decoration the colors are added before glazing. Blue and white porcelain, an important example of underglaze decoration, made use of a pigment known as cobalt blue - a form of cobalt oxide, which turned from black to blue when fired. The resulting effect ranges from a grayish or blackish blue to a sapphire blue, depending on the impurities present in the ore. Other common colors were obtained from antimony (yellow), iron (brown), manganese (purple) and copper (green). Overglaze enamels: Enamel colors were prepared from metallic oxides by adding the oxide to molten glass and reducing the cooled mixture to a fine powder which, when mixed with an oily medium, could be painted over the glaze and fused to it by firing. The oil burned out in the process. The range of colors obtainable by this method was greater than the range of underglaze colors, as they could be fired at lower temperatures - in the 1300 - 1750 F (700-950 C) range. Overglaze colors mature at varying temperatures, so that multicolored decoration might require a number of firings. Colored glazes: Since the 1750's some pieces decorated with different color glazes. The colors are created strictly by the color of the glaze. This method of decoration is not wide spread. Hand painting and transfer printing: Since the early 1750s, the transfer printing process used a metal plate on which the design was etched. The plate was “inked” with a metallic oxide bound in an oil-based fluid and was used to impress the design onto paper, which was then applied to the ware. During firing, the design from the paper sank into the glaze. Two techniques were in use - line engraving; and stippling with dots to produce light and shade effects. The engraved design was then transferred to “bats” of glue which were then pressed to the wares in order to transfer the image. Since the 1760s the underglaze blue printing replaced hand painting in the mass production of blue and white wares. From 1839 most of the multi colored wares used the transfer print technique. To distinguish printing from painting, look at the following: A painted pattern is made by brushstrokes, which shows greater fluidity than what can be achieved by printing. The use of a brush is most obvious where there is shading of color. Hatching is used to achieve a tonal effect in a print. (Look for dots or lines.) Hand painted pieces shows deviations typical of hand painting, where no two will be exactly the same. Gilding: Gilding is decorating with gold. Methods of gilding: Japanned gilding: Gold leaf was applied to the glaze using gum arabic and, after firing, was burnished, forming a thin, bright layer of gold. Oil gilding: Was used on some early soft-paste porcelain. Patterns were first outlined in a mixture of oil and gum arabic. The pattern was allowed to dry; then gold leaf was added and fired at a low temperature. Oil gilding is not durable and could not be burnished. Honey gilding: Continental factories of the 18th c. mixed gold leaf powder with oil of lavender and honey and applied the mixture to the porcelain with a brush. In this way layers could be built up and subsequently chased. Mercury gilding: In the late 18th c., a technique was evolved whereby gold leaf powder was mixed with mercury and applied to the porcelain with a brush. The mercury vaporized in firing, leaving a film of gold which could then be burnished to a brassy, bright finish. This technique allowed rapid decoration and was suitable for use with stencil, making it popular for services. 19th century gilding: Attempts to develop less expensive methods of gilding were made during the 19th c. Three important methods were (a) the use of gold leaf transfer prints (b) painting with liquid gold (c) the application of a paste after firing; this was then burnished. Marks Continental potters tended to apply marks to some of their products as early as the 17th century. Factory marks: Usually found on the base of an object. Variations in the precise form of a mark can provide a basis for dating. The marks may take the form of the maker's initials, the maker's full name, a symbol or coat of arms, or a combination of these elements. Painter's marks Some wares bear a small mark usually in the form of a numeral or symbol to indicate which decorator completed the design. A gilder’s mark also occur on some pieces. Pattern names and numbers: Pattern names: are often found on wares. Painted names identifying flowers or views usually indicate good - quality porcelain. Pattern numbers: were used to identify patterns. They are in the absence of a factory mark, can be of help in identifying makers. Type of marks: Painted marks: Most are applied after glazing and fired with the overglaze decoration. Printed marks: These are the most common form of 19th century marks, and are found both under and over the glaze. The mark is applied by means of a transfer either on paper or on rubber. Incised marks: These are signed into the body prior to firing. Much 19th century art pottery is marked in this way. Impressed marks: These are stamped into the clay prior to firing, using a metal die. Cast marks: These are found on molded wares where the factory mark forms part of the mold. Applied pad marks: These look similar to applied molded marks but are stamped onto an applied pad of clay. Authenticity Factors to consider when assessing the authenticity of a piece includes the following: Is the date suggested by the mark consistent with the date suggested by the shape and style? Is the piece formed by the appropriate method for the factory and the period? Is the mark consistent with the type of body? Is the mark correctly sized and positioned? Are the colors of the decoration consistent with original practice? Are the weight and size of the piece correct? Does the glaze look right? Is the piece appropriately irregular in appearance? Does it appear machine made? Does the piece measure up to the aesthetic standards of the factory to which it is attributed? Shapes and Style Basic shape of pottery and porcelain is important in the consideration of authenticity and value. The shape should be in line with all other indications pertaining to the age and maker. Some shapes are typical of the origin and represents the style of the era. The best representation of any style, would be lot more valuable than other pieces from the same time period. In many cases the style and quality of modeling is more important, than the age. (Example: fine “Art Nouveau” and “Art Deco” pieces are in higher demand than most wares manufactured from 1775 - 1850.) Condition As a rule of thumb only rare pieces can have noticeable fault or any restoration in order to be considered “good condition”. Look for wear on decoration, scratches and stains on the glaze, and chips or cracks of the body, and on the glaze. Most restoration will not restore the value, therefore should be considered as a damaged item. Re-golding is the most common restoration. It is very important to note, that hand made and good craftsmanship should not be mistaken with each other. There are different degrees in qualities of hand made, hand decorated, machine made or transfer printed objects. We should better ourselves in judging the quality of work. If we achieve a good understanding of different qualities, we will be able to judge the value and condition easier. Rarity Rarity is an important component of the value, but by no means the most important. Many rare, and even good quality objects, are not appreciated by the market. Typically the workmanship, popularity of certain styles and makers will determine value. At the same time, high quality items never in abundant supply. |
|
|
来自： 華登 > 《meissen porcelain》
