Applying a coating of tin to thin steel sheet either by dipping in molten metal or by electrolytic deposition (electroplating); almost all tinplate is now produced by the latter process, in which the tin coating is applied without heat. Essentially a sandwich in which the core is strip steel, tinplate has the strength and formability of steel combined with the noncorrosive and nontoxic properties of tin, and additionally is easy to solder. It is used for containers for food and beverages, paints, oils, tobacco, and numerous other products, as well as in toys, baking equipment, and parts for radio and other electronic equipment. Modern materials, including stainless steel and plastics, have replaced tinplate in many common applications.
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Formerly, tinplate was used for cheap pots, pans and other holloware. For many of these, tinplate has been replaced by galvanised (zinc-coated) vessels, though not for cooking as zinc is poisonous. Zinc protects iron electrolytically, that is, the zinc will oxidize and turn to a white powder to preserve the iron, whereas tin will only protect the iron if the tin-surface remains unbroken. This is why it is not safe to eat food from a rusty tin can.
This kind of holloware was also known as tinware and the people who made it were tinplate workers.
The first production of tinplate was probably in Bohemia, from where the trade spread to Saxony, and was well-established there by the 1660s. Andrew Yarranton and Ambrose Crowley (a Stourbridge blacksmith and father of the more famous Sir Ambrose) visited Dresden in 1667 and found out how it was made. In doing so, they were sponsored by various local ironmasters and people connected with the project to make the river Stour navigable. In Saxony, the plates were forged, but when they conducted experiments on their return to England, they tried rolling the iron. This led to the ironmasters Philip Foley and Joshua Newborough (two of the sponsors) in 1670 erecting a new mill, Wolverley Lower Mill (or forge). This contained three shops, one being a slitting mill (which would serve as a rolling mill), and the others were forges. In 1678 one of these was making frying pans and the other drawing out blooms made in finery forges elsewhere. It is likely that the intention was to roll the plates and then finish them under a hammer, but the plan was frustrated by one William Chamberlaine renewing a patent granted to him and Dud Dudley in 1662.
The slitter at Wolverley was Thomas Cooke. Another Thomas Cooke, perhaps his son, moved to Pontypool and worked there for John Hanbury. He had a slitting mill there and was also producing iron plates called 'Pontpoole plates'. Edward Lhuyd reported the existence of this mill in 1697. This has been claimed as a tinplate works, but it was almost certainly only producing (untinned) blackplate.
Tinplate first begins to appear in the Gloucester Port Books (which record trade passing through Gloucester, mostly from ports in the Bristol Channel in 1725. The tinplate was shipped from Newport, Monmouthshire. This immediately follows the first appearance (in French of Reamur's Principes de l'art de fer-blanc, and prior to a report of it being published in England.
Further mills followed a few years later, initially in many ironmaking regions in England and Wales, but later mainly in south Wales. In 1805, 80,000 boxes were made and 50,000 exported. The industry continued to grow until 1891. One of the greatest markets was the United States of America, but that market was cut off in 1891, when the McKinley tariff was enacted there. This caused a great retrenchment in the British industry and the emigration to America of many of those who could no longer be employed in the surviving tinplate works.
Despite this blow, the industry continued, but on a smaller scale. Nevertheless there were still 518 mills in operation in 1937, including 224 belonging to Richard Thomas & Co. However the traditional 'pack mill' had been overtaken by the improved 'strip mill', of which the first in Great Britain was built by Richard Thomas & Co. in the late 1930s. Strip mills rendered the old pack mills obsolete and the last of them closed in about the 1960s.
This was then rolled until it had doubled in length. The plate was then folded in half ('doubled') using a doubling shear, which was like a table where one half of the surface folds over on top of the other. It is then put into a furnace to be heated until it is well 'soaked'. This is repeated until there is a pack of 8 or 16 plates. The pack is then allowed to cool. When cool, the pack was sheared (using powered shears) and the plates separated by 'openers' (usually women). Defective plates were discarded, and the rest passed to the pickling department.
In the pickling department, the plates were immersed in baths of acid (to remove scale - i.e. oxide), then in water (washing them). After inspection they were placed in an annealing furnace, where they were heated for 10-14 hours. This was known as 'black pickling' and 'black annealing'). After being removed they were allowed to cool for up to 48 hours. The plates were then rolled cold through highly polished rolls to remove any unevenness and give them a sense polished surface. They were then annealed again (but at a lower temperature) and pickled again, this being known as 'white annealing' and 'white pickling'. They were then washed and stored in slightly acid water (where they would not rust) awaiting tinning.
The tinning set consisted of two pots with molten tin (with flux on top) and a grease pot. The flux dries the plate and prepares it for the tin to adhere. The second tin pot (called the wash pot) had tin at a lower temperature. This is followed by the grease pot (containing an oil) and removes the excess tin. Then follow cleaning and polishing processes. Finally, the tinplates were packed in boxes of 112 sheets ready for sale. Single plates were 14 inches by 20 inches; doubles twice that. A box weighed approximately a hundredweight.
What is described here is the process as employed during the 20th century. The process grew somewhat in complexity with the passage of time, as gradually it was found that the inclusion of additional procedures improved quality. However the practice of hot rolling and then cold rolling evidently goes back to the early days, as the Knight family's tinplate works had (from its foundation in about 1740) two rolling mills, one at Bringewood (west of Ludlow) which made blackplate, and the other the tin mill at Mitton (now part of Stourport, evidently for the later stages.
The strip mill had several advantages over pack mills: