Glass & enamel


Enamel & glass

The art of blowing glass probably developed in Syria in the first century BC. The basic techniques of glass blowing remained much the same for many hundreds of years, until mechanisation and blowing glass with compressed air took over the production of everyday products such as bottles, jars and tumblers. Blowing unique, decorative and quality glass items remains a skilled craft and the tools used by today's practitioners would be recognized by their medieval counterparts: paddles for protection from heat and to shape the glass, a marver for rolling the glass, jacks and shears for cutting and shaping, the blowpipe itself and the punty rod which is used to form the opening of a glass vessel.
A modern glass blowing workshop has three separate high temperature areas. The first is the melting furnace for producing the molten glass. This reaches reaches temperatures of 1150C. Once the blower has a gob of molten glass on the blowpipe, its temperature starts to fall. If it falls too low the glass becomes difficult to work and so is put into a glory hole, while remaining attached to the blowpipe or punty rod. The glory hole is a round chamber, well insulated with refractory material, used to reheat glass to keep it malleable. Once the piece is finished, it is placed into an annealing kiln or lehr to cool down to room temperature slowly without collapsing or cracking. This can take several hours according to the thickness of the glass.
Most glass is made from silicon dioxide. Adding other oxides into the mix changes the properties of the glass. For example, sodium dioxide increases viscosity and adds strength, lead oxide makes glass more brilliant. The deep blue colour for which Bristol glass was famed is derived from cobalt, while chromium makes glass green. Copper and silver can produce various colours. These same oxides are used to produce the colours in enamel, which is a thin layer of glass fused to metal.
Enamelling on precious metals to make jewellery, cups, bowls and other artefacts probably dates back to the beginnings of glass making. It was not until the early nineteenth century that enamel was applied to iron cooking pots. The advantages of a hard wearing, easy to clean and attractive bright finish were quickly recognised by manufacturers, advertisers and the emerging middle classes as enamelling spread to ranges, cookers, bathtubs and other white goods. While enamel may be a less popular finish in the modern kitchen, it is still widely used in industry for laboratory vessels, for signage and as a wall coating in areas of heavy traffic.

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