Introduction 31 –→ Table of Contents e) Factory mark and plaque number stamped into rear surface f) Lampshade is touched up prior to firing g) Kiln h) Storage cabinet for wax models any case, it was important to produce a “lean porcelain body” from “fine china clay” with the highest possible percentage of kaolin and a low content of the indispensable potter’s clay. An expert would describe this as “biscuit porcelain” because it originally underwent a very slow and careful double firing process without vitrification. “Biscuit” is a French term derived from the Latin biscotum, meaning “twice baked.” The chalkwhite body features a matt to satiny or full-gloss finish and can also exhibit slight roughness and porosity. The carefully guarded recipe for the newly developed porcelain body was the main secret behind the production of top-quality lithophanes. This material made it possible to create even the most delicate designs with no flaws or defects. Today, lithophanes are produced in only one firing, during which a sintering process in the body leads to vitrification. Manufacturers in English-speaking countries preferred the marblelike, semi-transparent soft-paste porcelain Parian to the porous and slightly rough biscuit porcelain. Parian has little or no porosity and is therefore smoother than biscuit. It was also particularly well suited for porcelain figures and for use in the slip-casting process. The English manufacturer Copeland & Garrett used the following recipe: Parian mixture: 24 parts frit 36 parts china clay 40 parts feldspar Composition of the frit: 57 parts white sand 11 parts Cornish stone (similar to Chinese petuntse) 8 parts potash67 The large number of British manufacturers (of Parian) used modified body recipes. It was the iron silicate in the feldspar that gave the Parian its final coloring, which ranged from light gray to cream; the higher the iron silicate percentage, the stronger the coloring. The first factories were established near deposits of high-quality china clay. It was also of existential importance that the factory had access to forests as sources of wood for firing the kilns and to running water for use in preparing the porcelain bodies and driving the machinery for grinding and mixing. This explains why most of the porcelain factories were concentrated in a small number of appropriate regions until the mid-19th century. Since then, technology and transport networks have developed to such an extent that the classic site requirements no longer apply. Some porcelain-makers contend that, owing to the high quality of modern ready-made bodies, it is now even possible to produce good lithophanes without specially formulated mixtures. However, this claim is not entirely accurate, as can be seen by the new porcelain lithophanes of varying quality that are available on the market today. Many of these are inferior to the 19th-century products. Producing the lithophane mold An essential step in the production of optimal lithophanes is the creation of a high-precision mold. The wax technique developed by KPM Berlin begins with the hand carving of an image in wax. An even layer of hard wax, approximately four to seven millimeters in thickness, is applied to a framed glass plate. This wax is generally beeswax mixed with white lead. Sometimes, other substances are added in order to improve the plasticity and transparency: e.g., whiting (washed chalk), stearin, or oils used in painting, depending on the requirements. The modeler, or “wax carver” (German terms: Gipsschneider, Wachsschnitzer, and Wachsstecher), then uses modeling tools to carve the image—generally copied from an original work of art—in freehand into the prepared sheet of wax on the glass plate, which is positioned at an angle and backlit (in transmitted light). The tools can be made of steel, ivory, horn, or wood and are similar to dental instruments. Stencils can be used to help transfer the image onto the wax, by marking the outlines. The lightest areas require deep carving, where the remaining wax can be as thin as approx. one tenth of a milli-
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