I want to buy this necklace but I need to know will it tarnish.

I am not sure what 'brass gold' is exactly but I suspect that it's a brass which has been mixed so that its colour matches gold. It will then be lacquered so that it won't tarnish too quickly, something like the way that a trumpet is made. 'Gold over silver' means that the chain is made of silver and gold washed or very thinly gold plated. Gold washing is a technique where a very thin layer of gold is deposited chemically. Gold plating means that the gold is deposited electrically and the thickness and the purity of the gold will be greater. Gold doesn't tarnish (though it is a soft metal and will scratch), so it will depend on how thick the gold plating is as to how long it will last.

With that question in mind, I suggest that you ask the seller that question. There is a feature on eBay sellers profile that you can use in sending them question regarding the product that they are selling. Most of the sellers are responsive on this feature especially when they want to sell the items immediately. Also, I suggest that you do not commit into buying the items, nor bidding on it without having your questions unanswered because chances are, you might end up with an item you never really liked. Good luck.

ah britzsofly, that is the question. gold in the lower price range are not usually gold after all. they are usually gold filled, or layered with gold and some other metal under it. it won't be worth anything. even don't are about that, it may just turn your neck green.