Ask Your Goldsmith:
I recently started to melt down some scrap gold into 8-10 gram lumps by using some high heat torches. Most of what I have melted is 10Kt and some 14Kt. I was just wondering if the 10Kt gold when melted this way is still 10Kt or am I burning off some of the alloys making it a bit higher. If you could give me some insight it would be greatly appreciated.
Thank you for you inquiry!
Yes, if you keep melting the alloy over and over again, part of the alloy burns off and surfaces! If you would pickle it in acid in between melting, it gets rid of the surface scale (mostly the copper of the alloy). Sulfuric acid diluted to half acid and half (or a bit more) water will be strong enough to get all the copper off the surface. Just make sure to put the acid slowly into water AND NOT THE OTHER WAY AROUND! One drop of water only would bring the acid to boiling point and the container may explode! To be safe, use "Sparex #2" granules only and dissolve it in water. It's available at any Jewellery supply store.
When melting gold scrap, as you told me, be careful not to get any impurities like lead solder or silver solder from earrings or chains into the melting pot. Check the old scrap gold, if it had been repaired and soldered by somebody with these types of solders, by handy home do it yourselfers ;-) One tiny bit of lead would destroy the gold and after that it has to be refined, because you can not work with that gold anymore until it is purified! It will get hard and pit marks and bobbles will appear. Gold has two "enemy metals" - one of them is lead and the other is mercury, which will dissolve completely when put together in a glass or stone bowl.
Also, gold solder will bring the KT down, because it is usually lower KT than the stamped gold from the "old days"! These days, the gold solder has to be same KT as it is stamped and trade marked. Chains for instance have solder on them on every link. In the old days, Gold made in the USA could be stamped 10 KT, 14 KT or 18 KT and be out by a half of one Karat. The Canadian gold goes by "Plumb Gold Standard" and the percentage of fine gold has to be right on, by all Gold KT Markings, followed by a registered "Trade Mark" to verify it.
In general usage, it means gold that has the same purity as the mark stamped on it. Therefore, 14KP means gold jewellery which had been soldered could be stamped 14Kt according to current US and Canadian Law, the pure gold content must be within 3 parts per thousand of the stamped karat mark for unsoldered items and 7 parts per thousand for soldered items. This means that technically all marked gold sold now "is plumb gold." In reality, not all gold jewelry is. When jewellers describe their jewellery as plumb gold, they are emphasizing that they abide by the law.
In the US and Canada, gold solders have also to comply with the plumb gold laws. A 14Kt solder might range from 12Kt to 14Kt. If jewelers want to specify that they want a solder which is actually 14Kt, they may request a plumb solder. When you have repairs done you should ask if they will use a plumb solder!
For more information, please read my other articles about Buying and Selling Jewellery, About Old Gold and Taking Care of Your Jewellery.
West York Jewellers