[header] How to buy scrap gold [title] Find the purity level. [step] Look at the stamp on a piece of jewelry, for example, and this will indicate whether it is 10 , 14 or 24 karats (it is only measured up to 24 karats). If there is no stamp you or a jeweler can use nitric acid to find out the real karat of a piece. 
There are nitric acid kits available to purchase online at such sites as amazon in order to do this yourself. To convert karats to a percentage, divide the karat number by 24 and then multiply it by 100.