http://www.tungsten-alloy.com/en/alloy11.htm This company is telling people that they could counterfeit gold with their alloy to make a believable gold coin or gold bar!
It would work, Assaying would not detect that. They would have to drill through the center of the gold bar in two spots to detect a counterfeit bar. Would make for an easy con, just go to a bunch of old farts and tell them you are an illegal immigrant and tell them that you would sell it to them for half the price per ounce of gold on a cash basis. make some story about how you cannot sell it through legal means since you are in the US illegally etc. The old farts eating dog food sitting on large cash nesteggs fall for this like dropping chum in an shark infested water.
"density of 19.25g/cm3 is just about the same density as gold (19.3g/cm3)" lol, thats not "just about the same density." Given the right equipment, any chem or physics 101 class can detect that difference.
No you do not have to do that. You can use Thermal Conductivity test, Magnetic Field test, Acoustic Resonance, X-Ray and more. So on the contrary, Assaying would detect tungsten.
Do all places do that? So when you buy gold on the internets where do you take it to do this and then if it fails what then? Makes buying gold risky
You are buying bullion coins aren't you? Drop the coin a few inches on a hard suface, it will ring with sweet notes like your other real coins do. If it thunks, you have a tungsten or depleted uranium slug. Just be careful what you say or do the next instant, you may be dealing with a real criminal... Of course you may scratch highly pure coins eg. .999 fine, if too eager on the handling, but bullion coins can be melted for content if necessary. Hopefully the Chinese will solve egregious people problems in their own usual way. The Chinese take their gold products pretty seriously and probably have little tolerance for fraud games. http://www.straitstimes.com/Breaking+News/Asia/Story/STIStory_413251.html For internet purchases you may need to do metal receipt in a controlled environment with the bank as observer of the transaction.
Many of the Chinese laborers who built the railroads in the Western US used to hollow out gold coins and refill them with lead. Then, they'd spend the coin and exchange the gold for another coin.
They did this with silver dollars too. Again the drop test will pick these up. Many vending machines even long ago used a combination of drop, as bounce, and electrical conductivity that would nail most fakes. That is why the post 1964 US coins used the copper sandwich when the Treasury started counterfeiting silver coins. High tech to squeeze a bimetallic sandwich, hard on the outside, softer but plenty conductive on the inside, these coins have a lower density (could nail 'em with size and weight if you didn't notice the copper edge).
And if it "thunks", do you think you can get your money back from whatever vendor sold it to you? Shouldn't have to take chances like that. In a related note, there are also websites dedicated to watering down toothpaste or making your own pet food using common household cleansers as well as instructional videos on how to change "3"s to "8"s and "1"s to "7"s for those pesky expiration dates on perishable products for your local bodega.