This might be useful.
It comes from "conservation advice" issued by the Australian War Memorial Museum.
Personally, I don't clean medals unless old polish residue needs to be removed because it is causing damage.
Cleaning medals
You may need to clean or even polish your medal before storing it.
However, we don't recommend polishing unless absolutely necessary because the repeated abrasion of polishing will damage the sharpness of the medal’s design. And polishing will quickly remove the gilded layer from gold-plated medals (for example, the Victory medal). Also, some polishes contain silicones which stay on the surface, making the application of a protective coating difficult and later cleaning more drastic than usual.
Note that when cleaning medals you should wear gloves and work in a well-ventilated area. Some of the chemicals are harmful if they touch the skin or are inhaled. Do not smoke when working with paints or solvents. Work out what you need and assemble everything before you start work. Allow enough time to work slowly and carefully, and to finish the job. For each stage of cleaning, first try the cleaning method on a small and inconspicuous area of the medal, for example part of the edge. If you are worried the treatment is harming the medal - stop.
First, take the ribbon off the medal by cutting the stitching, not the ribbon.
Degreasing the medal is the next step. This is done by dipping it in a small jar of acetone (available from your chemist or hardware store) and wiping it with a cotton bud. The acetone will remove most lacquers used to coat the medal. Using a soft child’s toothbrush moistened with water, work the brush gently in small circles to remove surface dirt. Work carefully, rinse frequently, and stop if the brush causes any scratching on the medal’ssurface.
If you think it necessary to polish the medal, use Hagerty's or Goddard's silver foam for silver or plate. Ensure that the foam does not contain silicone. If foam is not available, use Silvo silver polish or even silver dip. As silver dip etches metals, use it only if foam or polish is not available. Follow the instructions on whichever product you use. Make sure you remove all traces of polish after you finish - old polish residues look unsightly and can cause corrosion. Then dip the medal in methylated spirits and wipe it dry with cotton buds. Do not use Brasso to polish copper and brass medals. Brasso is more abrasive than silver polishes, and will remove more metal and design details. The polish residues left from Brasso can be very difficult to remove.
www.awm.gov.au/about/our-work/projects/medals
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