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yuuyaku@ηΦ–ς
KEY WORD :@art history / crafts
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Also yuu ηΦ or uwagusuri. Glaze. In the heat of firing, clay particles vitrify to form a glass matter capsule,himaku ”ν–Œ which covers ceramics to make them non-porous, gives added strength, and provides gloss to the surface. Glazes are differentiated in several ways: by firing temperature, koukadoyuu ‚‰Ξ“xηΦ (high firing glaze) and teikadoyuu ’α‰Ξ“xηΦ (low firing glaze); by appearance, toumeiyuu “§–ΎηΦ (transparent glaze), futoumeiyuu •s“§–ΎηΦ (opaque glaze), tsuyakeshiyuu ‰ΑηΦ (matte glaze), irogusuri FηΦ (color glaze) and kesshouyuu Œ‹»ηΦ (crystal glaze); and by ingredient, tetsuyuu “SηΦ (iron glaze), douyuu “ΊηΦ (copper glaze), enyuu ‰”ηΦ (lead glaze), chousekiyuu ’·ΞηΦ (felspathic glaze), kaiyuu ŠDηΦ (ash glaze) and soudayuu ƒ\[ƒ_ηΦ (alkaline glaze). Basic ingredients are silicic acid, aluminumoxide, sodium, kalium, calcium and magnesium, with lead, zinc and other metals added for some glazes. Old pottery glazes are divided into alkaline glaze, lead glaze and ash glaze. Lead glaze, common since the Han dynasty in China, is found in on ryokuyuu —ΞηΦ (green glaze), sansai ŽOΚ and Japanese *rakuyaki ŠyΔ.
Ash glaze, developed as a natural glaze in China, deploys wood ash or lime which melts evenly at 1200 C. The color of most glazes depends on the type and amount of metal content, the oxidation, deoxidization or neutrality of the firing process, and the properties of solvents. For instance, iron glaze fires to black, brown, amber or yellow; copper glaze fires to green, red or blue; and manganese glaze fires to purple, black, cobalt or indigo blue. Changes in color or texture that take place during firing are called youhen —q•Ο (kiln changes).
In Japanese pottery glaze serves not only a practical sealing function but also is an integral part of the aesthetic appeal. Most Japanese pottery is made watertight by high firing, only the lead glaze on earthenwares serves as a sealant. Early pottery, except for lead-glazed sansai ware of the 8c, utilizes natural glazes and is thus classified as "unglazed." Although usually created by a mix of glazes, they are generally described as having ash glazes. There are three types of ash glaze: pure wood ash, which may be added by hand or created through natural kiln precipitation or contrived precipitation as in *bizenyaki ”υ‘OΔ, *shigarakiyaki MŠyΔ and *igayaki ˆΙ‰κΔ@; ash combined with iron-rich ochre clay to produce reddish brown opaque glazes kakiyuu Š`ηΦ; and minerals added to wood ash including wood ash poor in iron oxide for porcelain glazes, wood ash with iron oxide for ki-seto ‰©£ŒΛ, yellowish to reddish brown and black iron glazes ameyuu ˆΉηΦ, and wood ash with pulverized brass for oribe glaze *oribeyaki D•”Δ. Feldspar and pegmatite are also frequently used minerals. Shino glaze *shinoyaki Žu–μΔ is made only of feldspar. Wood ash and rice-straw ash are also used together in such glazes as douseiji “ΊΒŽ₯ (a bluish green opaque copper glaze), and shirahagi ”’”‹ (the bluish white or sprinkled blue of *hagiyaki ”‹Δ). Many other glaze effects can be achieved by adding wood charcoal or salt during the firing, or by the arrangement of pots in the kiln.
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