Now that we have a better understanding of what silver tarnish is, we can talk about what causes silver tarnish. The rate that silver tarnishes is a function of temperature, humidity, and chemical exposure. In general, if these factors are low, then you can reduce the amount of tarnish. Silver in cool & dry environments will tarnish slower than in high moisture.
As we mentioned before, silver sulfide is the main result of the silver tarnishing process. While moisture is required for the tarnishing reactions to take place and oxygen plays a role in the reaction that creates silver sulfide, hydrogen sulfide is the main culprit. If you come in contact with material that contains sulfide compounds and then get those on your silver items, you will see that silver tarnish. For example vegetables from the Allium genus like onions or garlic contain organic sulfur compounds that , while low in concentration, could contribute to tarnish.
From reading articles on various sites, the copper portion of sterling silver can create copper oxide or possibly copper sulfides. You can check out an interesting debate about copper tarnish on pennies at Finishing.com. From working with copper, I have seen it tarnish considerably faster that sterling silver. We have polished a piece of silver and a piece of copper, and the copper has tarnish on it sometimes in as little as under an hour. Fine silver tarnishes slower than sterling silver. Is the copper the reason sterling silver has the potential to tarnish more easily? There are definitely some more questions I have about how the two materials interact and tarnish in combination.
In addition, chemicals have an effect on the rate and amount of tarnish. Ever jump into a pool with your silver jewelry on? You may have found the silver tarnished fairly quickly and in some cases almost instantly. In this case the cause could be the chlorine content in combination with the acidity that produces a silver chloride. With personal care products for skin and hair, coupled with other fragrances we spray on, the list of potential contaminates that can effect tarnish can get pretty long.
Even our bodies can play a role. A lot of times you may hear people say that skin composition can effect the rate of tarnish, I think it really is the composition of a persons sweat. Perspiration is water containing sodium chloride, phosphate, urea, ammonia, ethereal sulfates, creatine, fats, and other waste products. Eww! Sounds gross, but it does highlight that our bodies are part of the equation. Your own perspiration composition changes with various factors such as diet, health, and hormones levels. I found another discussion on Finishing.com that talks about body chemistry and silver tarnish
The last thing we have observed is that tarnish begets tarnish. If you have a clean piece of silver that isn't tarnishing much and put it in contact with another tarnished item, the tarnishing seems to accelerate. We have seen this happen on necklaces. The tarnishing rate has increased on other cleaner charms and on the chain if it is sterling silver when the tarnished charm was added to the arrangement. I can't explain technically what's going on or the roll perspiration has, but it is something we've confirmed empirically.
Next we'll tackle the discussion of what can be done to clean and prevent tarnish.