Tin pest (or 'tin plague', 'tin disease', 'tin leprosy') is an annoying process that affects things made out of tin, such as organ pipes. In scientific parlance, tin pest describes the slow transformation from metallic tin (the allotrope1 known as white tin or beta tin) to another, non-metallic2, form of tin (grey or alpha tin). This transformation, however, only takes place at temperatures below 13.2°C - above that temperature the metallic form of tin is stable. The process is autocatalytic, meaning that the transformation becomes faster as more and more of the non-metallic tin is formed.
Tin pest would be of minor importance were it not for the fact that church organ pipes were often made of metallic tin, which is a ductile material with a comparatively low melting point. In the colder regions of Europe the metallic tin would slowly 'degrade' to the non-metallic form, which is a worthless and brittle material. The individual pipes would get out of tune increasingly quickly (because of the autocatalytic nature of the process) and after a while get destroyed (because of the brittleness of the non-metallic tin). The term 'tin pest' emerged in these communities more than 500 years ago.
Note that the tin pest is not a form of corrosion; tin does not become oxidised in any way in the process (tin pest also takes place in vacuum). Tin pest describes a reaction3 taking place within a solid material, hence it is a very slow one (on a timescale of years depending on the initial quality of the tin used). There are two ways to circumvent tin pest:
- One is to keep stuff made out of tin in places with temperatures above 13.2°C.
- The other one, which alchemists figured out via 'trial and error' soon enough, is to add small amounts (0.1-10%) of lead, antimony or silver forming a tin alloy that is stable against tin pest. Tin pest does not play a significant role today4.
Napoleon's Buttons and Scott's Expedition
Two tales are commonly associated with tin pest. The first one claims that one of the problems in Napoleon's Army was that the soldiers' clothing had tin buttons. According to that tale the buttons degraded due to tin pest during the Russian Campaign, aggravating the soldiers' situation5 in the famous winter of 1812. The other one is that the expedition of Robert Scott to the South Pole in 1912 faced serious problems on their way back from the pole as the solder of the kerosene canisters deployed in depots degraded due to tin-pest leaving them out of kerosene.
Both tales are probably urban legends. Soldiers' clothing in Napoleon's Army relied primarily on wood buttons. In the case of Scott's expedition there are two arguments against the tin pest tale: First, expeditions to chilly places were not uncommon, and Scott himself was an experienced leader of expeditions. If tin pest played any role in the degradation of food or fuel canisters this would have been well-documented. Second, none of the expedition's canisters found in 1957 showed any sign of tin pest.