Hi Andy,
If your cement is epoxy resin, I can tell you that it is a combination of organic and inorganic compounds that can be removed by a 50:50 ratio of acetone and water. The acetone is great organic solvent and water removes inorganic species. Mix the acetone and water together and you have a solvent that can remove most unwanted chemical compounds. Use a wooden toothpick dipped in the solvent and apply to the area. The wooden toophpick should not damage the badge and the patina to the other parts of the badge should not be affected. This method is also valid for removing verdigris (copper salts) from your brass badges. As with any method, try the mixture on a dud badge first.
Safety when using the solvent described above: Acetone is flammable so keep away from sources of ignition. It is also mutagenic. Wear safety glasses and gloves at all times.
Let us know how you get on.
Cheers,
Gaz
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