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Transfer Printing & Flowing the Blue
In ceramics decoration, a pattern or picture can be applied either under or over the principal glaze. Underglaze decoration is generally regarded as a superior method because the underlying pattern is effectively sealed under a protective, hard glaze. The earliest contacts with China brought back to Europe the highly prized hand-painted Chinese Blue and White porcelain; an underglaze decoration in deep blue covered by a clear, hard glaze. The Chinese had discovered centuries earlier that the blue color, brought about by the use of cobalt, could withstand the high temperatures required for the firing of porcelain. It took the English over a century before they could emulate the Chinese Blue and White porcelain.
The technique of pattern transfer (transfer printing), invented in the mid-1700's, involved using a metal plate (almost always of copper). The plate was first engraved with the desired design. It was then warmed and cobalt oxide paint was rubbed into the design. Damp tissue paper was then applied directly onto the plate. The tissue was then carefully lifted from the copper plate and pressed onto the bisque pottery. When correctly placed, the "transferrer" would rub the tissue with flannel. The tissue was then floated by placing the bisque into a tub of water, leaving the transferred design behind.
As mentioned above, the transferred design had to be carefully treated to avoid border flaws and other imperfections from becoming too obvious. The salt-glaze earthenware that was used to mimic the brilliant white Chinese porcelain was porous, and early potters of this technique discovered that the cobalt oxide would actually diffuse slightly around the design. The design would also blur when the outer glaze was applied. This produced a mild hazing effect that would tend to mask any design application or other flaws. It was this effect which was later enhanced with the actual development of flowing the blue cobalt.
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