What Pliny says of the colour and weight of those minerals that produced tin, corresponds exceedingly well with tin ore, which, as is well known, is among the heaviest of minerals, though the specific gravity of the metal itself is but small. It is also true that lead is seldom found without silver; and tin perhaps has never been found with the latter. What we read in regard to the obtaining of tin ore, agrees very well with our washing-works. Even at present the greater part of the tin ores are found in fragments and washed.
The smelting of this metal, even when all the rules of art are not employed, is attended with little difficulty, though Goguet is of a different opinion. As of all metals it melts easiest in the fire, it requires only a small degree of heat and no artificial furnace; but as it is readily calcined, and after repeated reduction loses its malleability, care must be taken that the reduced metal can immediately flow off; and on that account our furnaces have an aperture always kept open. It is probable that the ancients, in their small furnaces, could easily make a similar arrangement.
Tin at all times must have been dearer than lead, as the latter was found in abundance, but the former in small quantities. In England at present tin costs about four times as much as lead. At Hamburg, in 1794, a pound of English block tin cost eleven schillings and a half, and tin in bars thirteen schillings; but a hundred pounds of English lead were worth at that time only fourteen marks, and Goslar lead eleven and a half marks ready money.
That tin melts easier than lead is very true. According to the latest experiments the former fuses at 442°, whereas lead requires 612° of Fahrenheit’s thermometer. Both metals can be fused in paper when it is closely wrapped round them. Aristotle and Pliny meant to say the same thing of their paper; and the latter adds that the paper, even when it became torn, was not burnt. What the first says of melting in water, some have too inconsiderately declared to be a fable; but it is not entirely false. Tin, when mixed with lead and bismuth in certain proportions, is so fusible that it melts in boiling water, because it requires less heat to be fused than water does to be brought to a state of ebullition. That the Celtic tin contained a great deal of lead, appears from the observation, that when rubbed it made the fingers black; an effect which would not have been produced by pure tin.
That tin in the time of Pliny was mixed with lead, and in various proportions, we are told by himself. At that period a mixture of equal parts tin and lead was called argentarium; and that of two parts lead and one part tin, tertiarium. Others mixed the latter composition with an equal quantity of tin, and named the mixture also argentarium, and this was commonly used for tinning.
I must, however, acknowledge that the last words of Pliny I do not fully comprehend. They have not indeed been noticed by any commentator; but I do not on that account believe that I am the only person to whom they have been in part unintelligible. Savot and Watson[530], who were undoubtedly capable of giving some decisive opinion on them, have purposely left that part, which to me appears obscure, untranslated and without any explanation. Pliny says, “Improbiores ad tertiarium additis æquis partibus albi, argentarium vocant, et eo quæ volunt, incoquunt.” He seems here to throw out a reproach against those who melted together equal quantities of tertiarium and pure tin, and then gave it the name of argentarium, as if it had been of an inferior quality to the argentarium first named. But equal quantities of tertiarium and pure tin produced a mixture, in which for one part of lead there were two of tin. How then could those who made this mixture be called improbiores? To answer this question I shall venture to give my conjecture. Pliny perhaps meant to say, that tinning properly ought to be done with pure tin, but that unprincipled artists employed for that purpose tin mixed with lead. If this be the true meaning, his reproach was not unfounded. On the same account, because all tin was then adulterated with lead, Galen gives cautions against the use of tinned vessels, and advises people to preserve medicines rather in glass or in golden vessels. But why does Pliny add, “ideo album nulli rei sine mixtura utile?” In using these words, it is possible he may have alluded, not to tinning, but to things cast of tin, which, according to the ideas of that time or the nature of the tin, if of that metal alone, would be too brittle. This seems to be said by the preceding words, to which the ideo refers: “albi natura plus aridi habet, contraque nigri tota humida est, ideo album....” I hope the reader will forgive me for entering so deeply into criticism; but if Pliny’s valuable work is ever to become intelligible, occasional contributions of this kind must not be despised.
Of the process employed in tinning in ancient times, we have no account; but the words of Pliny incoquere and incoctilia seem almost to denote that it was performed, as in tinning our iron wares, by immersing the vessels in melted tin. It appears also to have been done at an early period in a very perfect manner, both because the tinned articles, as Pliny says, could scarcely be distinguished from silver, and because the tinning, as he adds, with an expression of wonder, did not increase the weight of the vessels. The metal, therefore, was applied so thin that it could make no perceptible addition to the weight. This is the case still, when the work has been skilfully executed; and it affords a remarkable proof of the astonishing divisibility of metal. Dr. Watson caused a vessel, the surface of which contained 254 square inches, and which weighed twenty-six ounces, to be tinned, and found that the weight was increased only half an ounce; consequently half an ounce of tin was spread over 254 square inches.
But, notwithstanding all this dexterity, which must be allowed to the Romans, they appear to have employed tinning at any rate for kitchen utensils and household furniture very seldom. It is scarcely ever mentioned, and never where one might expect it, that is to say, in works on cookery and domestic œconomy, where the authors give directions for preparing and preserving salt provisions. When they speak of the choice of vessels, they merely say that new earthen ones should be employed. Some of the physicians only have had the foresight to recommend tinned vessels. It does not appear indeed that the Romans, though copper vessels were in general use among them, employed any precautions to prevent them from being injurious to the health. Pliny only says that a coating of stannum improved the taste of food, and guarded against verdigris. The former part is to be thus understood; that the bad taste occasioned by copper was prevented; but he does not say that the health was secured by it. The term also incoctilia, usual in the time of Pliny, is found in his works alone. It is likewise remarkable, that among the numerous vessels found at Herculaneum, as I have already remarked, the greater part of them were of copper or stannum, few of which were silvered, and none tinned. Had tinning been then as much used as at present, some tinned vessels must have been found.
I shall further remark, that Pliny ascribes the invention of tinning to the Gauls; and that he extols in particular the work of the Bituriges, the old inhabitants of the province of Berry, and those articles made at Alexia or Alegia, which is considered to have been Alise in Auxois; that he speaks of tinning copper and not iron, and that according to his account not only tin was used for that purpose, but also stannum. By the passages already quoted, it is proved that in the time of Homer cassiteron was employed for ornamenting shields and certain kinds of dresses; but the further illustration of them I shall leave to others. The shields perhaps were inlaid with tin; and it is not improbable that threads were then made of this metal, and used for embroidering. That this art was at that period known may be readily believed, since the women of Lapland embroider their dresses, and particularly their fur cloaks, in so delicate and ingenious a manner, with tin threads drawn out by themselves, as to excite astonishment[531].
What Pliny says is true, that lead cannot be soldered without tin, or tin without lead. For this operation a mixture of both metals, which fuses more readily than each of them singly, is employed. Instead of oil, mentioned by Pliny, workmen use at present in this process colophonium, or some other resin.