Quote:
Originally Posted by MikeK
The original composite cork gaskets were bonded with vulcanized latex. Vulcanization is a cross-linking process that uses sulfur. Those gaskets would, upon gradual deterioration, out-gas sulfur dioxide. Sulfur dioxide reacts with silver to produce the classic silver tarnish that starts light yellow and progresses to black.
Back in the day coal was king in heating buildings and steam powering trains and industry. Because of the high sulfur content of most coal the atmosphere had quite a bit of sulfur dioxide that also contributed to silver tarnishing.
A lot of people mistakenly believe the yellow to black silver tarnish is oxidation. It is a sulfur reaction. Silver oxide is white and does not occur with atmospheric exposure at environmental temperatures.
Modern composite cork is bonded with a modified butyl compound and does not out-gas sulfur compounds. They have no affect on silver. Also, today's atmosphere is very low in sulfur compounds so silver reflectors need far less maintenance than they did in the Model A era.
A polychloropene ('Neoprene') gasket is relatively unreactive and does not out-gas any oxidant compounds. It will not directly react with silver or aluminum. Uncoated polished aluminum will react with oxygen in a damp atmosphere and oxidize to a grayish surface in a few months.
Brattons aluminized reflectors are overcoated with a silicate compound that isolates the metal surface from the atmosphere.
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Very interesting. Do you have any information about atmosphere, pollution, and nickel plating? My replated for 15 year (2005) radiator shell is holding up much better than my original plated (1929) headlights did before 1950. Also my plating since 1980 seems to be holding up pretty well too.