NC - that's a really nice find. I'm no expert but I'll throw my $0.02 in there. I wouldn't do anything more with this button. It looks like most of the silver gilt is already off it. Further cleaning with ammonia soap, water, vinegar, lemon juice will probably just mess it up. The green is tarnish that is basically erosion as brass ages (this button was probably silver plated brass). Any additional soaking may take off the letters. Another potential problem with soaking - that button looks to be a two piece button which means the top was pressed in a die and mated to the bottom half. The button loop actually went into the button and was probably attached to a paper spacer. If your button has any pinholes or openings, by soaking, you're going to allow the liquied to get inside. Eventually this liquid will corrode the button from the inside out - you'll either get pin holes, larger holes or the button will crumble. If you want to clean some of the corrosion or dirt on the back, try a wooden toothpick...just be careful...a needle with a magnifying glass may work but use a scraping motion .....you don't want to punch through the button. If you leave some of the dirt on there it will actually highlight the lettering in back and some of the features in front. One final thing, when handling buttons put your fingers on the outer edges not on the top and bottom...if it's a fragile two piece, you could collapse the button. If you find another with gold or silver gilt, make a mixture of 50/50 lemon juice and water, use a q tip to gently brush the mixture on the top of the button....just leave on for 30 seconds or so....use a clean q tip to brush off with water...you can brush on baking soda to make sure you neutralize the lemon juice then clean that with water on the qtip....I would say soaking is a no/no....just some thoughts...if you put that in a case, try to not have any pressure on the button itself.
