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alloys, pewter

Значение термина alloys, pewter в knolik

alloys, pewter - Alloys, Pewter
alloys, pewter - (a) Pewter is an alloy of lead and tin, containing sometimes copper, zinc, or antimony. There are three distinct kinds of English-made pewter, viz.: (1) Plate pewter, used for dishes and plates, an alloy usually made without lead, and containing principally 90 parts tin, 7 antimony, 2 bismuth, and 2 copper; (2) Trifle pewter employed for casting drinking vessels, etc., an alloy of 82 parts tin with 18 lead, and containing variable quantities of antimony; and (3) Ley pewter, containing 4 parts tin and 1 lead, employed for the larger wine measures. Owing to the poisonous nature of lead, which is apt to be dissolved by the acetic acid always present in beer, the French Government has prohibited the use of an alloy containing more than 16½ per cent, of lead; if the lead be not in excess of this quantity, the tin seems to have the effect of neutralising its poisonous properties. When made in the above proportions, pewter has a specific gravity of 7.8, so that any specimens of a higher specific gravity than this may be known to contain too high a percentage of the heavier metal. Pewter is a soft metal resembling tin, but duller and darker in colour. Plates and dishes are hammered out of the variety called plate pewter, but drinking vessels, etc., are always cast into moulds from the common variety. (b) Analysis of various samples showed the following compositions:

Quality of Pewter	Tin	Lead	Copper	Anthimony	Zinc
Ordinary	82	18	..	..	..
Good	88.5	..	4.5	7	..
Good	89	..	2	7	..
Good	78	11	8.25	..	2.25
Better quality	85.5	..	..	14.5	..
Hard	90.57	..	1.88	7.55	..
Plate	89	..	2	7	2 Bithmuth

(c) The following is a brief extract from a paper read before the Society of Arts by Mr. P. S. Liberty. It is still questionable, I believe, what were the precise alloys and the relative proportions used in the manufacture of ancient pewter; and, indeed, down to our own day the word "pewter" has an elastic meaning. I gather, however, that some among the old examples show a large admixture of lead, as, for instance, a vase-handle of the 4th century of our era, dug up in Rome, which, according to Bapst, was assayed in France early in the last century and found to contain about three-sevenths lead, without any trace of copper. This must, therefore, be considered as of very inferior quality. By way of explanation, it has been suggested indeed, that tin procured with difficulty from a remote and barbarous region was almost as dear as silver, and that this may account for the low grade of pewter being in use in Rome. On the other hand, however, Mr. Gowland's analysis of varying examples of Roman pewter shows that the question of cost was by no means invariably considered. His results give for what he terms "typical Roman pewter": 72.36 tin to 26.90 lead, and 70.58 tin to 27.62 lead, that is, to put it roughly, three parts tin and one part lead.

According to Mr. Welch, in the ordinances of the old English craft of pewterers, two qualities of pewter are described, the first of tin with a small admixture (supposed to be about 5 per cent.) of what is called " kettle-brass," otherwise known as "peak" metal, the peak metal being a compound of copper with some other metal not definitely ascertained, and probably always kept a mystery of the Guild. The second quality was originally called "vessel of tin," being a compound of tin and lead in the proportion of 1 cwt. of tin to not exceeding 26 lb. of lead. This alloy was afterwards known as "lay " or lead metal. In the present day, and of late years many experiments have been made and various modifications have been tried in the composition of pewter, nearly every manufacturer having his own particular formula. For the production of modern pewter goods aspiring to be classed as artistic in design the inferior alloy containing lead is discarded altogether (except by the Japanese in the manufacture of their antimony ware). And to avoid as far as possible, the use of copper, which some consider to have a bad effect on the colour, tin is nowadays alloyed in the proportion of about 5 per cent, of antimony or bismuth, or both. An excess of copper imparts a brownish tint, whilst the use of lead (always be it remembered the alloy of the so-called second quality pewter) imparts the well-known grey-colour tone which, be it acknowledged, has for some of us a decided charm. Still, as we know, if lead is used beyond a certain proportion, it renders the pewter dangerous for the use of liquors containing acids such as beer, wine, vinegar, etc., by reason of the chemical action they set up, the excess lead producing poisonous oxides.

The old pewterers appear to have had one advantage over the modern in the fact that their lead nearly always contained a small percentage of silver, and the fascinating lustre which many old pieces of pewter possess is generally ascribed to the presence of this small proportion of silver in alloy. Modern German pewter, as compared with modern English, contains a much larger proportion of antimony, with some bismuth, and gives out when bent or bitten (which the modern English does in a far less degree) the well-known distinguishing crackle or cri.

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