top coat absorption

[keifer kahn]

I purchased a zinc based silver F&R tank badge about 3 years ago.When i first received it .it had a few holes and patches in the top finish where the top silver finish had been absorbed by the base metal( leaving a black colour in each hole and patch).I looked at it recently and the absorption seems to have increased quite rapidly,and there seems to be twice as many holes and patches as before.Ive always had the badge stored in an airtight plastic sleeve.Is there any way to stop this,or is it just part of that time deterioation process?
Regards keifer

[Frank Heukemes]

Dear Keifer,

Maybe it reacts to the plastic of your ziplock sleeve?

Cheers, Frank H.

[Mike Coleman]

You have to be very careful with plastic materials used as long term storage. Some plastics are fairly inert but others (most) can be quite reactive. It is often difficult to tell by looking or handling the material what you have and you usually have to get the material in manufacturerer's packaging to tell. Rule of thumb is hard plastic is better than soft (such as zip lock bags). The problem is with chemicals that make up the polymers are often halocarbons or carbon compounds that contain halide ions such as chlorides, florides, etc. Many of these compounds will form gasses that contain these elements as the plastic "cures" or ages. If you poke your nose near the plastic and it smells like "plastic" it is giving off compounds that you don't need. This is actually an important issue these days because of all the man made materials in homes and offices that make folks sick ( so called sick building syndrome)This process can occur for years after the manufacture of the material. Some of these will combine with zinc to form zinc salts that then cause areas of corrosion or spotting on the plated surface. Remember that grossly the plated surface may look solid but under an electron microscope a thinly plated surface is full of defects. Late war plating was pretty thin in places. Also any wear areas will open the plating. Once this process starts it can be like a cancer and eat up the plating over the years. With zinc badges that have any wear at all this process is going to happen in almost any environment, the only difference is the rate at which it will happen. I have watched this occur to some of my badges over a 30 year period left on an enamaled metal shelf and dry room air. The only way to prevent it is to remove the piece from an oxygen rich environment such as placing the piece in an airtight glass container filled with nitrogen or some other inert gas - not too practical for most of us. All this gets abck to the concepts of preservation, conservation, restoration and repair which I won't get into. This was long winded but hope it was of use. Mike C.

[keifer kahn]

thanks for the great info.guys.The badge on the back is fine with no deterioation at all,apart from the very dark, almost black blue zinc colour,but the front has certainly deterioated wherever there is plating applied.you certainly can tell its silver by the black colour in each hole and patch.
i know that none of us want our items to diminsh in anyway,but i suppose,looking on the brightside,at least if they deterioate according to the characteristics of known genuine pieces,then it is just adding to our authenticity checklist!

Thanks heaps guys,
keifer kahn