I picked up a desk medal recently that is bronze-plated tin. It's got some wear and has been harshly cleaned in the fields, exposing the light orange bronze. The rest of the metal is a very dark patina except where the wear has passed through the bronze into the tin. I've got it sitting out on a shelf in my office right now, standing on edge against an old book binding, but is there a better way to help the fields retone to the same dark patina as the rest of the bronze? I've always been one to leave things as they are, but with the harsh cleaning, I don't think I can hurt this further.
That's tough. You'd want something that affects copper but not tin, in that case. I don't know offhand if sulfur will work or not. There's always the old "stick it in an envelope on the windowsill/radiator" method, I guess.
A quick google search doesn't turn up any an reactions between metallic Tin or Tin Oxide (I don't know if there is a surface oxide layer) and Sulfur at room temps. Tin Oxide minerals are brown so that is a good thing. I like Paul's suggestion of putting it in an envelope (I read that the yellow envelopes have the most sulfur). Just check it frequently to make sure you don't get some funky chemistry. It's a cool medal which would definitely benefit from some toning, but I would hate to screw it up You said the base metal is tin. If it's pure tin, you should be aware of "tin pest". Tin can change crystal structures when exposed to low temps, which will cause it to crumble. Once the reaction starts, it will speed up. The American Plantation Tokens of the 1680's suffer from this.
I like the window sill method. Lay it out in the open on a piece of cardboard. It's never going to even out but the light areas will get darker. ...awesome coin BTW, absolutely a beautiful design. Too bad about the cleaning but history is history. It's always worth preserving.
I found this paragraph while I was Googling sulfur compounds. This doesn't sound too good: Sulfur dioxide is used as a preservative in dried fruit to prevent it from spoiling, and also to preserve the fruit's gorgeous and appetizingly bright color. That's why unsulfured fruits tend to look brownish or black. It sounds gross, but sulfur dioxide is a gas that's created by burning coal or oil, which both contain sulfur. This gas smells similar to rotten eggs and though used as a food preservative, it's also used in products as disinfectant or bleaching agents.
It is a nice piece and a rare medal. The fields don't look nearly as nice in hand as they do in the photos. The hairlines and color are more severe. It would definitely look more attractive with a darker color in the fields, even if it doesn't get as dark as the rest of the patina (also darker than in the photos), but I don't want to get too drastic. I think leaving it for some time in a yellow envelope sounds about right. I'm not in a hurry. I just want to make sure I'm leaving it in an environment that will darken the fields over time. If anyone else has suggestions, please chime in as well. Thanks. Sent from my SM-N910V using Tapatalk
The medal was probably "antiqued" as issued. If you're not a fan of the surfaces as they are now, try re-applying an antiqued finish.
