Gold Density Machine

Gold testing of gold is one fraught with difficulties and although it may on the surface seem simple to test for pure gold it is actually far more difficult than it first seems. Indeed any comprehensive test is in most cases a destructive process, something which collectors of gold coins and gold jewellery in particular will want to avoid

A look at pure gold in natural light can be indicative as well, gold should keep its colour in the shade and in direct sunlight, pure gold should not glitter unlike a number of other metals. There are though a number of other metals that have the same characteristics as pure gold, and a sight test will only show up the most obvious fakes

Gold is not a hard gold so there are a number of hardness tests that can be done, although these can result in a partial destruction of the real gold item. A sharp pin should dent a real gold item but will break if the metal is harder than gold. The same theory also applies to a bite test, a bite should mark the gold but again metals like lead will produce the same results. Historically a useful guide was the streak test in which a piece of gold was rubbed across a piece of unglazed porcelain, a yellow mark indicates gold and a black mark would be produced by pyrite, again though other metals will produce a yellow mark.

Recent fake gold items have been found out by a simple magnet test, gold is not magnetic but then again there are also plenty of other metals that aren't either.

If you know a friendly jeweller you could ask them to look over your item an experienced eye may be able to discern a fake, but by no means is this a hundred per cent accurate.
In most cases I would recommend that the best and simplest method of testing for pure gold is to undertake a density test. Pure gold should have a density of 19.32gm/cm^3, and can be easily worked out using a scale to weigh the gold and then using a graduated cylinder of water to measure how much water is displaced once the gold item is placed into the water. Density works out as mass or item divided by volume

The density test is by no means full proof though, and tungsten for example has exactly the same density as pure gold. An unscrupulous person may well fake a pure gold item by placing a layer of pure gold around a tungsten centre, tungsten costing a fraction (about 1/40th) of the price of pure gold. For small items, like gold coins, then it would be not cost effective for someone to fake an item but for gold bars it does become a possibility.

All of the methods above are relatively simple and cost effective, and although some are destructive they make up the best options for testing a small number of small items. Conclusive tests can be achieved with more expensive testing though.

Simple acid and electric kits are available and will show gold items simply, but do require the use of a pure gold sample, so a piece of the gold item is destroyed, not much good for gold coin collectors looking for mint items. A melt-and assay test, also known as a fire test requires that a sample is destroyed, although it does result in a very accurate result for the make up of the sample. Kits and testing for these methods normally cost in the region of GBP50 although prices do vary around this figure.

If destruction of a sample is not an option then there are two other methods, an X-ray Fluorescence Analysis test, but costs GBP5000, and a GBP30000 Inductively-coupled plasma mass spectrometry test requiring x-rays, a vacuum and electron beam. Accurate results are produced but are out of the question for most small time collectors.

The purchasing of pure gold can be a gamble although for gold coins the density test still makes the best sense, but it is not a certain method. There is a certain amount of trust involved, but most collectors of any item know this feeling.

http://www.helium.com/items/1384824-how-to-test-for-pure-gold?page=1