Old Sheffield Plate (OSP) is the material developed by Thomas Boulsover in the 1740s, a fusion of copper and sterling silver which could be made into a range of items normally made in solid silver. The material rapidly gained popularity as a substitute for solid silver, as it was much cheaper to produce. Any object made in silver could be made in Old Sheffield Plate, although objects subject to heavy wear such as spoons and forks were not so satisfactory in plate. The characteristic identifying feature of OSP is the 'bleeding' or 'show through' of the copper base, especially on points of wear. There is also a subtle difference in colour between the pure silver of electroplating and the "very faintly bluish lustre" of OSP. In addition to having a distinct bluish cast, the alloy produced in OSP is also harder than electrodeposited silver. The material remained popular until being replaced by the electroplate process in the 1840s. Items produced in Old Sheffield Plate included buttons, caddy spoons, fish slices, serving utensils, candlesticks and other lighting devices, coffee and tea sets, serving dishes and trays, tankards and pitchers and larger items such as soup tureens and hot-water urns. 'Old Sheffield Plate' with all three words capitalised is the accepted term in the antiques trade for this material. The expression 'Sheffield plate' and all variations thereof are generic terms which may apply to any product of silver appearance made in Sheffield, UK.
History
Boulsover's discovery
The fact that silver and copper could fuse together was almost certainly well known to Sheffield silver makers, as silver based solder (an amalgam of silver, copper and zinc) was widely used. Boulsover's discovery or invention was to find that sheets of silver and copper under high pressure would fuse together when heated to the melting point of the silver-copper eutectic alloy, then could be rolled out and shaped without the layers separating. The material could be rolled out to a thinness appropriate for the making of silver items. As far less silver was needed, the price of these items was far lower. The material was invented by Thomas Boulsover, of Sheffield's Cutlers Company. It was said that while trying to repair the handle of a customer's decorative knife, he heated it too much and the silver started to melt. When he examined the damaged handle, he noticed that the silver and copper had fused together very strongly. Experiments showed that the two metals behaved as one when he tried to reshape them, even though he could clearly see the two different layers. Although it was certainly Boulsover who discovered the commercial viability of fusion, it is unlikely that the accidental discovery is any more than an anecdote. Boulsover set up in business and carried out further experiments in which he put a thin sheet of silver on a thick ingot of copper and heated the two together to fuse them. When the composite block was hammered or rolled to make it thinner, the two metals were reduced in thickness at similar rates. Using this method, Boulsover was able to make sheets of metal which had a thin layer of silver on the top surface and a thick layer of copper underneath. When this new material was used to make buttons, they looked and behaved like silver buttons but were a fraction of the cost.
Two cities The main centre for the trade was always Sheffield, England, where there was already a substantial manufacturing industry for making small silver items such as buttons, cutlery and snuff boxes etc. Following Boulsover's discovery, the trade rapidly expanded particularly from the 1760s onwards. The other centre of production in England became Birmingham, almost entirely through the efforts of Matthew Boulton. While Boulton's ormolu and solid silver products tend to attract most attention, his button and plated wares manufacturing were financially always more important.
Later practice Following the invention of German silver (60% copper, 20% nickel and 20% zinc), around 1820, it was found that this new material also fused well with sheet silver and provided a suitable base metal for the Sheffield process. Because of its nearly silver colour, German silver also revealed less wear, or "bleeding", when Sheffield-made articles were subject to daily use and polishing. Being much harder than copper, it was used from the mid-1830s but only for articles such as trays or cylindrical items that did not require complex shaping. After about 1840 the Sheffield plate process was generally replaced with electroplating processes, such as that of George Elkington. Electroplating tends to produce a "brilliant" surface with a hard colour – as it consists of pure rather than sterling silver and is usually deposited more thinly. Sheffield plate continued to be used for up to a further 100 years for silver-plated articles subject to heavy wear, most commonly uniform buttons and tankards. During the 1840–1850 period, hybrid articles such as sugar bowls were produced, with the body being Old Sheffield Plate and complicated small parts such as the feet and handles made from electroplate. These are rare and seldom recognised. The Sheffield plating process is not often used today. During the Second World War, a process analogous to Sheffield plating was used to build intercoolers for Rolls-Royce Merlin engines to overcome problems with thermal fracturing.
Techniques
Double plating Double plating or sometimes the 'double sandwich' form of Sheffield plate was developed around 1770. Used for pieces such as bowls and mugs that had a visible interior, it consisted of a sheet of silver each side of a piece of copper; early manufacturers applied a film of solder over the bare edge of copper although such pieces are very rare. Edges of early salvers were hidden by folding them over but from about 1790, borders were applied with U-shaped lengths of silver wire to conceal the copper which can often be felt as a lip on the underside. Towards the end of the period, solid wire was sometimes used which can be hard to see.
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