Guyton’s Survey of Platinum Cladding

In 1811 Guyton surveyed the various methods that had by then been used for platinum cladding, and he included a description of the vessel given to him by Chabaneau (9). It was in the form of a shallow bowl, 75 mm long, 52 mm wide, 14 mm deep and 0.78 mm thick at the rim. It weighed 34.505 grams. Its specific gravity was 11.44, and, as it contained only platinum and copper, with specific gravities of 21 and 8.87 respectively, he calculated that it contained 23.4 per cent of platinum and 76.6 per cent of copper by volume. (Guyton had, in fact, miscalculated, for the correct answer is 21.2: 78.8.) Thus, he said, the platinum contributed just over a fifth of the total thickness, about the same as that of silver in silver-clad copper. (He was referring to silver leaf hammered on to heated copper in several layers and then burnished.) Gold as well as silver could be used in this type of cladding, called “plaqué”, and it is clear from Guyton’s account that this was the method used by Chabaneau for platinum.

Guyton pointed out that copper could also be coated with gold by covering it with gold amalgam and heating to drive off the mercury, or by dipping it into a solution of a gold compound (auric chloride) in ether. Both these methods were covered by the term “dorure” and he coined the word “platinure” for similar procedures that had been used for platinum. There was some doubt about the existence of platinum amalgam, but Guyton was convinced that in 1798 he had prepared it in a solid form by boiling platinum in mercury for two hours (10) and in his 1811 paper he referred to others who had apparently obtained it.

In 1797 Apollos Mussin-Puschkin added sal ammoniac to a solution of platinum in aqua regia, ignited the precipitate—ammonium chloroplatinate—and ground the platinum sponge so obtained with mercury in a mortar (11); he continued to work on these lines, using the amalgam for the preparation of malleable platinum by driving off the mercury by heat, until his death in the year 1805.

In a letter to N. L. Vauquelin, written in Madrid in 1803, J. L. Proust described how platinum sponge, formed in the same way, dissolved in hot mercury (12) and in a footnote added to the published letter Fourcroy and Vauquelin stated that platinum sponge would dissolve in cold mercury to form an amalgam (13).

The Strauss Coating Method

Guyton recorded Proust’s observation that the amalgam could be spread on copper and would make it possible for the copper to be coated with platinum, but it is not clear from Proust’s letter whether he in fact succeeded. Coating by this method was, however, done in 1803 by a German called Strauss, who could not have known about Proust’s suggestion. All we know about Strauss is that he came from Asschaffenburg, a town on the River Main, and was working at Erfurt in the private pharmaceutical institute that was founded in 1796 by J. B. Trommsdorff (14) and was quite separate from the university, where Trommsdorff was a professor of chemistry. About three hundred students passed through Trommsdorff’s Institute before his death in 1837; they received practical as well as theoretical instruction in chemistry, pharmacy and related subjects and aimed to become pharmacists, doctors, teachers or manufacturers (15). It was in a journal edited by Trommsdorff that Strauss described how he coated copper with amalgam (prepared in a way similar to Mussin-Puschkin’s), heated it to drive off mercury, and then added another layer of amalgam mixed with a little chalk and moistened with water. A second heating left the copper with a coating of platinum that shone like silver when burnished and was, by virtue of its hardness and resistance to reagents, superior to the tin with which copper was commonly plated (16).

James Stodart of London

Guyton, in his 1811 paper, now drew attention to the work of James Stodart of London, who in 1805 used a solution of a platinum salt in ether. It was well known, said Guyton, that when a solution of gold in aqua regia was shaken with ether the gold compound—auric chloride—dissolved in the ether and the solution left a covering of gold when applied to another metal. In his important early account of platinum, William Lewis stated that a solution of platinum in aqua regia was unaffected by ether (17), but in 1805 Stodart found that in fact it behaved similarly to gold; the ether extracted a platinum salt—platinic chloride—and if polished iron, steel or brass was dipped into the ether solution it became coated with platinum (18). In collaboration with his friend “Mr Hume, chemist, Long-Acre”, Stodart had already perfected a method for gilding iron and steel in this way (19), and he thought that gold would generally be preferred as it was more beautiful than platinum. He added, however, that he achieved beautiful effects by coating different parts of the same instrument with gold and platinum. Stodart, a cutler, was probably referring to surgical instruments, which he made and sold at his shop at 401 Strand, opposite the Adelphi. The little that is known about Stodart’s life has been published by Hadfield, who was unable to find a portrait (20). Stodart was interested in chemistry and metallurgy, and spent much time on attempts to improve steel. About 1818 he began to collaborate with the young Michael Faraday, preparing steel containing platinum and other noble metals, and this research led to his becoming a Fellow of the Royal Society in 1820, at the age of sixty. Faraday lost his enthusiasm for this work when Stodart died three years later.

Guyton’s 1811 article contained no original observations, but his full summary of earlier work may have stimulated interest in platinum cladding, at least in France. In the same year the Society for the Encouragement of National Industry awarded a prize to Messrs. Levrat and Papinaud for their competence in producing gold- and silver-clad copper objects of high quality by the traditional method of hammering gold or silver leaf on heated copper. They also showed the Society a platinum-clad vessel, presumably made in the same way, that was stated to be “large and without any imperfection” and completely resistant to attack by the three mineral acids. Levrat and Papinaud employed thirty workmen, but their establishment at 66 Rue de Popincourt, in the working-class area of Paris not far from the site of the Bastille, had room for two hundred. They were therefore in a position not only to increase their production of gold and silver plate, but also to supply platinum-clad vessels to chemists and pharmacists (21). It is however, by no means certain that there was a real demand for such vessels, and it may be significant that at exhibitions organised by the Society in 1813 and 1814 they displayed only gold and silver plate, and no platinum (22).

The Society was, however, still interested in platinum cladding and in a report of the 1817 exhibition stated that the platinum prepared by Cuoq, Couturier and Bréant, whose work has been described by McDonald (23), could be beaten into very thin leaves. The reporter, Mérimée, suggested that it would produce very agreeable effects if used in conjunction with gold leaf; he said that silver and gold could not be used together because the silver rapidly blackened, but that platinum did not have this defect (24). It will be recalled that Stodart had earlier obtained such “agreeable effects” with gold and platinum applied by the ether process.

Although all the processes described so far had appeared in print, they were unknown to Thomas Thomson, professor of chemistry at Glasgow University, author of a well-known textbook and editor of the monthly Annals of Philosophy, in which he wrote in December 1819: “I am not aware that any process for covering metals with platinum has yet been published”. Thomson was replying to an enquiry by T. Howse, senior, of Cirencester, who had heard from a chemical friend that some copper articles coated with platinum, in the proportion of fifteen to one, could be purchased for about 37 shillings a pound from Monsieur Labouté, of 4 Rue St. Eustache, a street in the Montmartre district of Paris that has now disappeared. Howse did not know how the coating was done (25); his own attempts to use an amalgam had failed, but Thomson, in his reply, expressed the opinion that such a method should be possible (26).

In fact Labouté, who was also known as Michaud (27), did not use an amalgam. On 24 January 1818 he and a co-worker called Jean Dupuis were granted a patent for ten years for an elaborate process in which heated copper was first coated with silver leaf and platinum was then applied on top of the silver after burnishing, rolling and re-heating (28).

The letter Howse sent to Professor Thomson shows that Labouté’s ware was put on sale, but there is no evidence of the scale of production and it is not known whether any other manufacturer took advantage of the expiry of the patent in 1828.

Platinum-clad vessels never seem to have been used in the kitchen, and chemists and manufacturers preferred apparatus made of solid platinum. Dr. C. Bromeis, of Hanau on the River Main, became interested in the use of platinum in jewellery, a local industry, and during the trade depression following the revolution of 1848 he described methods of mechanically coating copper and silver with platinum as an economy measure (29). However, it is unlikely that his proposals were adopted for by this time electrolytic methods had been introduced for both gilding and silvering and the relatively small demand for platinum plating was also satisfied by electrodeposition (30).