The cannon may have had a protective coating that was removed after firing and cleaning. The coating prevented tarnish and corrosion, but the brass is now unprotected and free to react with the environment. Sulfur in black powder would likely be a bad actor with the brass.
It would be interesting to know if the spots show up at the same location and shape after cleaning. If the spots truly reappear, then there could be segregation in the brass making local areas more susceptible to discoloration.
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Larry Hanke FASM
Principal Engineer
Materials Evaluation And Engineering Inc
Minneapolis MN
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Original Message:
Sent: 11-03-2020 15:23
From: John Shingledecker
Subject: Brass Cannon 'Spots'
This is a bit off-the-wall, but I was passed this question from a hobbyist who is faced with 'spots' - I assume its corrosion on his brass cannon. I do not have details on why he has a brass cannon and how often he fires it, but he provided this account and some pictures. I have no experience with brass or cannons so thoughts appreciated. Arm-chair metallurgy encouraged :)
- - -
... I appreciate you taking interest in my dilemma. If possible, I would appreciate if we could find out cause and any possible solution to prevent spotting from reappearing.1. I have had the brass cannons for 8 months with no problems with finish(probably cast in last 2 years) and only after firing cannon using black powder -then cleaning/washing it, does problem appear.
2. Once spotting begins, you can remove the spots completely without much effort with Brasso, but will continually reappear over the next 1-2 days.
3. Does not feel raised.
Thanks for your assistance.
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John Shingledecker FASM
Electric Power Research Institute
Charlotte NC
(865) 201-1252
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