Looking on Google to try and resolve this discussion, and to start with I couldn't find any mention of pewter and cold.
First I looked at the various types of pewter and found that:- "Going back to the 15th century, by then it appears that by then there were three 'recipes' of pewter regulated by the Guilds. The first type, known as fine metal was used for flatware. It consisted of tin with as much copper as it could absorb, which is about 1%. The second type, known as trifling metal or trifle, was used for holloware. It is made up of fine metal with approximately 4% lead. The last type of pewter, known as lay or ley metal, was used for items that weren't in contact with food or drink. It consisted of tin with 15% lead." And also:- "Pewter is an alloy composed primarily of tin with varying quantities of hardening agents such as antimony, bismuth, copper and lead. It was used in the ancient world by the Egyptians, Romans and other civilisations and came into extensive use in Europe in mediaeval times. Tin was alloyed with copper and bismuth and the resulting metal, although now much harder than pure tin, still possessed a low enough melting point to make it easy for casting. Later, the ordinances of The Worshipful Company of Pewterers laid down the composition of the pewter alloy, originally in two grades of fine and lay metal. Fine was used for sadware â plates, chargers, etc. â and for spoons and ecclesiastical flagons whilst lay metal was used for hollow-ware â pots and measures. Lay metal contained a higher proportion of lead which was used as a low cost bulking agent and help durability." Oxidation was harder to find out about as it is mostly the term used to describe the deliberate (or eventual by time) dark finish used as a patination on some pewter. However I did find a reference to:- "Oxidation on pewter varies according the composition of the alloy and even this composition can vary on individual pieces. Serious oxidation can eat right through the metal and eventually create holes,....." And finally:_ "Although buying pewter so dull and tarnished that its complexion is similar to that of a dirty blackboard usually has a happy outcome, one should be wary of pieces that show signs of serious corrosion. This could be the result of being stored in a place where it was damp, such as a cellar or a shed with a leaking roof, or, if a plate, being used under a potted plant. Such corrosion can be so extensive that even after skilled treatment with an acid bath or by buffing, the surface is badly pitted. There are likely to be fine pinholes, too where the corrosion has gone through the metal." I now did a search for pewter and corrosion (the magic word) and struck gold:- "Pewter should be kept in clean and not too humid surroundings. In a high relative humidity the oxide film grows thicker and the corrosion accelerates even more when dust settles on the surface. Dust contains corrosive salts, which keep the surface humidity high. The thick oxide layers can be seen on tin coffin plates from damp and dusty crypts and old chapels. The superficial tin oxide, which bears the inscription, can then easily flake off in thick layers. Archaeological items of tin can be totally converted to oxides. From archaeological marine sites it has been noted (2) that pewter containing some proportion of lead can survive under certain conditions. A special form of corrosion on the insides of basins and ewers for baptising is caused by deposited calcium carbonate (limestone). If kept damp the carbonate coated tin surface will corrode. There is another deterioration phenomenon that should occur in pure metallic tin, and in tin with a limited amount of lead, at temperatures below 13°C. The metallic tin should change to a grey crystalline powder. This allotropic structure change is normally referred to as tin pest and is described by Hedges (Hedges, E.S.: Tin and Its Alloys, Edward Arnold publishers Ltd, London, 1960, pp 16-37, 50-72.). Proving the phenomena by analysis is however difficult, because mostly tin oxide is detected. Deterioration seems to start locally in spots or as lines where there is stress in the metal from bending or pressure. The attack is first seen as small volcano shaped craters opening on the metal surface. This is because the change results in expansion. The produced powder drops out of the craters, leaving holes. The preservation of tin ware starts by keeping it in a clean, dry, indoor climate above 13°C. Handle it with cotton gloves." As our house it often below 13°C at night, and I don't intend to wear gloves to make lace then my bobbins will have to take their chance. I will do my best to keep them dry <VBG> Regarding the infectious nature of corrosion, I suppose it is possible that if the corrosion was caused by salts, and the affected piece touches and passes them to another, then that piece could also corrode. Jacquie in Lincolnshire - To unsubscribe send email to majord...@arachne.com containing the line: unsubscribe lace y...@address.here. For help, write to arachnemodera...@yahoo.com
