Gold is considered to be one of the most costliest metal, Gold is an inevitable material for all occasions in Indian tradition.As we know that Gold prices are rising day by day, Gold merchants are trying to make the most of it by cheating the customers i.e by providing them less quality of gold.
We have many devices to measure purity of Milk, to check the status of our health but we do not have a perfect device to test the purity of gold. Though there are some vague methods which can be used to test gold but there isint any standard device.
Quality of Gold
- When we say 24kt or 24K gold jewelry, we mean that all the 24 parts in the gold are pure gold without traces of any other metals. This is considered 99.9 percent pure. 22K gold means that 22 parts of the jewelry are gold and the remaining 2 parts are some other metal. This is considered 91.3 percent pure. 18K gold means that 18 parts of the jewelry are gold and the remaining 6 parts are some other metal. This is equal to 75 percent pure. The purity goes down from there, with each karat equaling approximately 4.1625 percent.
- In gold that is less than 24K, the other alloys in the item give it hardness and color. We can state that 24K is the softest and 10K the hardest, because 10K would have 41.6 percent gold and the balance would be other metals, which are harder than gold. The color from the other metals enhances the beauty of the jewelry, such as you see with white gold, yellow gold, red gold, etc.
- 24K is pure gold but generally too soft for use in jewelry or coins. Because of this, other metals are added for consistency and this makes for different densities.
- The markings are a bit different on gold jewelry made in Europe and indicate an item’s purity. The markings are typically three digits and are as follows:
- 10K 417 marking: gold purity is 41.7 percent
- 14K 585 marking: gold purity is 58.5 percent
- 18K 750 marking: gold purity is 75 percent
- 22K 917 marking: gold purity is 91.7 percent
- 24K 999 marking: gold purity is 99.9 percent
How To Evaluate the Purity
Properties of Gold
Gold is a soft metal. It is very malleable, corrosion-resistant and generally does not cause skin reactions. From any chemistry text book you may understand that gold has a melting point of 1064 degrees celsius and a boiling point of 2808 degrees celsius.
As gold is very soft, jewelers mix copper, silver, palladium and nickel to harden it. The gold you see in your jewelery is actually gold alloy. The alloy ingredients will influence the final colour of the gold — nickel would produce a whiter tone than copper, which will produce a yellow metal.
Carat and Purity
Now we can try to understand a few interesting facts about the metal we all cherish so dearly. The purity of gold is measured in Carats. The term Carat was used hundreds of years ago in the Middle East. Caratage indicates how pure the metal is.
The gold Carat (ct) tells you how many parts of gold and how many parts of other metals are in the alloy. Jewelry standards specifies the benchmarks for gold to ascertain its fineness i.e., parts per thousand. For example your 24 Carat gold is considered to be 999.999 parts per thousand. One carat is one part of 24, or 41.66 parts of a thousand.
Now you may understand the basis that there can never be a total and absolute purity of gold. Your22 Carat gold is 22/24th (gold is 916.000 parts per thousand and other metals have 84 parts). Your 18 Carat gold is 18/24th (gold is 750 parts per thousand and other metals have 250 parts). Similarly your 14 Carat gold is 14/24th or 585.000 parts per thousand and other metals have 415 parts. Your 9 Carat has this ratio: 9/24th (gold is 375.000 parts per thousand and other metals have 625 parts). This system of calculation gives only the weight of pure gold contained in an alloy.
Acid Test Kits and Electronic Testing Kits
You can test the purity of gold yourself with the right test equipment. The acid solutions are marked with various Carat gold strengths, usually 22K, 18K and 14K. A touch stone is a ground black glass sheet or similar. What you need to do is go through the surface of the gold by using a file or blade in an INCONSPICUOUS place.
File or cut into it a small amount and then place a drop of, say 9K acid, directly on the cut. If no reaction then it is at least 9K. Use the next highest acid (say 14K). If no reactions, then try 18K acid. No reaction? Then you know it’s at least 18K gold. If some reaction, say the cut turns brown, it is less than your acid strength. Proceed to apply lesser strength acids till there is no reaction.
Bear in mind however that any testing with chemicals will mean a loss of some small amount of gold. Electronic testing is now becoming popular and electronic testers can be found with a little investigation, research, and money. Testing gold is a great way to determine purity.
Hallmarking of Gold
Now let me discuss hallmarking. A hallmark is a purity certification of gold articles in accordance with Indian Standard specifications. India Bureau of Indian Standard (BIS) was named as the sole agency in the country for Hallmarking gold under the provisions of the BIS Act, 1986. BIS is primarily engaged in the preparation and promotion of standards and operation of different quality certification schemes. You might have noticed hallmark seals placed on gold ornaments and jewels in jewelry houses.
The hallmark is comprised of five elements
- BIS Mark
- The fineness number (corresponding to given caratage)
- Assaying and Hallmarking Center’s mark
- Jeweler’s mark
- Year of marking denoted by a code letter and decided by BIS (e.g. code letter ‘A’ was approved by BIS for year 2000, ‘B’ being used for the year 2001 and ‘C’ for 2002).
The marking is done either using punches or a laser marking machine. Its purpose is to safeguard the consumers. The meaning of this mark is that the assayers (an independent body – assay office) guarantee the legal standard of fineness or purity. This mark applies for both buying and selling of ornaments and jewels.
Hallmarking is a reliable certification. But its implementation is not complete in all respects. Fashionable jewelry is sometimes less reliably hallmarked. So be cautious. While buying gold check it yourself or have it checked by a professional. LASTLY, I would like to point out that I am not a jeweler and the above guidelines are not provided out any expertise.
Mahesh ( MGIT ECE 4th year )
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