Purity of Gold

For high accuracy a sample would be run by an analytical chemistry laboratory.

For a reasonable estimate of the Karat value see a jeweler. They have a simple test.

That simple test is just within 10% and in the jewellers favour, as you would expect.

There have been a number of counterfeit gold bars found. Usually they use a cheap metal like tungsten as a core and cover it with gold. It got so bad they were drilling bars that had the exact correct specific gravity, but were 10% gold. They found these when industrial buyers went to melt and ingot and found this solid core of tngsten.

Then they perfected the ultrasound method that shows the transition easily and put a stop to it.

Once you get to high densities, like gold. You have a hard time making a faked bar that passes the archimedes test. A list of the elements shows this in grams/cc

tungsten 19.600

uranium 18.900

platinum 21.400

plutonium 19.800

gold 19.320

lead 11.340

mercury 13.593

molybdenum 10.188

platinum 21.400

plutonium 19.800

silver 10.490

As you can see you have only very few candidates to use to make a low cost faked gold bar. There were a number of faked gold bars made in the 70's that passed the archimedes test, but were 95% Tungsten cored. They found that an ultrasonic tester would show the transition between the gold cladding and the tungsten core and all bars are now tested.

There are also a number of numismatic forgery cases with rare collectible gold coins being copied very well in pure gold. Detection of these fakes is usually by looking at trace metal elements in the gold and comparing this to the ratio of the coins produced by the original mint

hai

thank you foryour mail

i would like to know if there's any non distructive test to find the purity

the one available is using laser which is very castlier.

the second is using the arcemedis law but the accuracy is less

what i want to if there's any special property of gold so that wecan develop a system according to that

thanking you

sun

Laser is OK with a plating, but does not tell the bulk. The fakers are quite good.

http://www.google.ca/search?hl=en&q=fake+%2B%22gold+bullion%22&btnG=Google+Search&meta=

Sun

The purity of gold is usually determined by a method called "Fire Assay", Basically the gold (and its alloying or impurity) metals are alloyed with lead a high temperature (1100 degrees Celsius) The molten lead oxidises to form litharge and this along with the base metals like copper and zinc are absorbed in to a porous ceramic cup called a cupel. By a quirk of nature the molten precious metals have a higher surface tension and are not absorbed into the cupel, where they remain as a molten bead. On cooling this bead is taken from the couple and rolled out very thinly, this is then usually coiled and dropped into hot dilute nitric acid which removes the silver. The gold that remains (as long as no platinum group metals are present) is the annealed at about 800 degrees Celsius which consolidates it and it shrinks in size to form a coil called a cornet. By knowing the start weight of the impure gold and the weight of the pure gold cornet the purity of the gold can be calculated. The result in normally expresses in carats, where 24 carats is pure gold, therefore 18 carat gold contains 18/24^ths or 75.00 % by weight.

For very high purity gold the impurities are measured and the gold is determined by difference. This is not the whole story, but gives the basic idea.

I hope this helps!

Chris

dear chris thank you for the notes it's good enough to get the basic knowledge but when you wnat to make something to check the purity of an ornament, we need some special properties of gold.and it shold be a non distructive test. you cannot expext your wedding ring to be cut in to pieces to know the purity (we will never cut the wedding ring as we are sure about the purity of love and affection behind is 100%). so we want to know how gold like material's reaction to certain frequencies or something like that but unique thanking you sun

sun

Weigh you ring accurately in air and then in water, you will have to suspended it by a very thin nylon thread. This will enable you to calculate the rings density (look on web for details) I think that pure gold should have a specific gravity (density) of about 19.3

Regards

Chris

PS

There are instruments such as x-ray spectrometers that can do the analysis non-destructively

If the density of the gold sample is less that the pure gold specific gravity of 19.3, what factor do you need to apply to it to calculate the percaentage of Gold in the sample. What i do know is that a factor of 5.096 is multiplied by the density to give a purity percentage.

im not a scientist; what is this 5.096 factor, whats its relevance and how is it applicable?

by determining the density and then the 'purity' using the above method, the purity is expressed as a percentage, and applied to the gold samples 'air weight' to come up with the actual weight of the real Gold that you then pay for.

is this correct?

If the density of the gold sample is less that the pure gold specific gravity of 19.3, what factor do you need to apply to it to calculate the percaentage of Gold in the sample. What i do know is that a factor of 5.096 is multiplied by the density to give a purity percentage.

im not a scientist; what is this 5.096 factor, whats its relevance and how is it applicable?

by determining the density and then the 'purity' using the above method, the purity is expressed as a percentage, and applied to the gold samples 'air weight' to come up with the actual weight of the real Gold that you then pay for.

is this correct?

HOW IS THE PURITY OF SAY A GOLD RING DETERMINED AS WHEN YOU TAKE IT TO A PAWN SHOP?

THANKS

The best way would be check "Archimedes Principle" of doing it. The cheapest and the most accurate way.

Archimedes Density Method is however the only solution but it is strictly applicable to the binary alloys of known metals. If it is still unknown as to what metals are alloyed with gold, no unique solution is possible.

We have been working on this problem for a long time. We also discovered a workable solution but none is ready to believe us. Our findings are likely to publish in 'Material Letters' an ELSEVIER B. V. publication of international acclaim. The Article is however in Press but online since 7th Nov. 2006.

We do neither intend any more to advertise our Research paper for sale nor the software itself. We are not in search of any Rewad/Award but we are quite annexious and serious to know whether the work we have carried out is of any scientific value or merit. The abstract of the Research Paper my be found at the link given below.

We invite you for serious discussions and expect scholarly comments from scholistic readers. We are unable to paste the 'Paper' online since the Copy Rights have already been transferred ro the Publication Group. Still for further information regading our findings one may contact us.

Dr. B. C. Rathore

Theoretical optimisation of constitution of alloys by decoding their densities
Materials Letters, In Press, Corrected Proof, Available online 7 November 2006
B.C. Rathore, Pratibha and Bharati doi:10.1016/j.matlet.2006.10.052

We are glad to inform you that the research paper entitled "Theoretical optimisation of constitution of alloys by decoding their densities"
has now been published and may be tracked at the following link:

Materials Letters
Volume 61, Issues 14-15, June 2007, Pages 2956-2960

(Dr. B.C.Rathore)