Hi Onepixel,
silver reacts on hydrogen sulfide, it's a gas that is present everywhere. Humans also produce this gas.
These materials contain a lot of hydrogen sulfide: wool, rubber, latex, some perfumes, onions, eggs (if concentrated, hydrogen sulfide smells like rotten eggs).
It has nothing to do with the quality of your silver, it happens to all unrhodinated silver. I have been noticing the same thing lately.
Your skin also releases substances that make silver react: alcohol, medication influence the acidity of your skin. When sweating, you'll produce amonia that will intervene with the acidity of your skin, and then cause a reaction on the silver. High skin acidity makes silver oxidize more easily.
I remember that long ago my grandparents would say that if you wear silver, and it gets black easily, it means that your liver is not working as it should be.
I know there's a connection between hydrogen sulfide and CFS/ME. People with leacky gut and a deranged colonic flora can produce more hydrogen sulfide (a neurotoxin), which results in several complaints. Too high amounts of hydrogen sulfide affect the nervous system and disturbs oxigenation conditions what will lead to many symptoms like fatigue, loss of appetite, headaches, irritation, bad memory and dizziness.
These are the findings of my dr - this is one of the goals he sets for each of his patients: reducing the production of hydrogen sulfide through elimination of certain foods, determination of food allergies and intolerances, and restoring colonic flora.
I think this is a very interesting subject... 
Post Edited (MarieLS) : 3/21/2013 2:31:11 AM (GMT-6)