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War medals are tarnishing

Suggestions required on how to keep silver WW1 and WW2 medals from tarnishing.All these medals are in a glass covered display. All medals have ribbons which cannot be removed. What acid (hopefully HCl as that's so easily available!) should one use for precleaning & wetting out the surfaces and for how long and in what concentration?  Should one perhaps preclean with a conventional polish and THEN acid dip? Some medals are just brass with, one assumes, a previous protective coating or have an enameled finish. These should not be 'cleaned'. Most  are silver which tarnishes over time. Will an ordinary varnish be OK? Any suggestions will be gratefully received.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
1999

I would suggest doing the silver with a "dip type" cleaner/polish. Some of these also will shine up brass; I'm not sure what to do with the enameled ones. Maybe you could contact a military museum for restoration suggestions. After they are cleaned and shiny, put a VCI sponge in the case. These are sponges that emit a gas that deposits on the metals to prevent corrosion. We use them in systems at the sewage treatment plant to prevent corrosion of control systems.

Gene Bennett
- Everett, Washington
1999