Though it does bear resemblance to certain Civil War Navy and Marines buttons, it is 99.99% not Civil War as it is not listed in Tice's "Uniform Buttons of the United States, 1776 - 1865" (the button Bible). Also, with all do respect, I'm slightly confused by the comment that if it has no backmark, it's impossible to tell. Unless the face is totally destroyed the button can very easily be identified. In fact, a lot of buttons don't even have backmarks. To clean, I use 80% lemon juice combined with water and soak for 2 - 5 minutes. Then let soak in olive oil for a few hours. Hope this helps.
[/quote
I agree with you,on all but......I would not recommend putting a two piece button in any oil as you will have a mess for a long time!!!!!