"Fire Black" Corrosion/Tarnish of Silver
Country: United Kingdom
Date: Fall 2012
I am a secondary school teacher of Design Technology in the UK. When at college, many years ago, I am sure that I learnt the term "fire black" for the corrosion (tarnish) that forms on the surface of silver. I have checked the search engines on the Internet and I cannot find a reference to "fire black" or indeed any other term than just "tarnish" for the black oxide that forms on silver. Is my memory at fault?
I have never heard of the term "black fire". I should point out that the
black tarnish that forms on silver, is not silver oxide. It is
caused by sulfur emissions from burning of fossil fuels that contain
small amounts of sulfur.
Silver doesn't tarnish only with oxygen, but involves sulfur to make silver sulfide which is black. There is a trace amount of sulfide in air, like SO2, and when you burn silver there is an oxidation of silver with sulfur to produce silver sulfide. Even without burning, you can see the color of silver products (silverware, jewelry, etc) turns black when they are old. This is also an oxidation of silver with sulfur in air.
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Update: November 2011