The carat (abbreviation ct or kt) is a measure of the purity of gold alloys, 24-carat being pure gold. In the United States and Canada, the spelling karat (abbreviation k or kt) is used.
Measure
Carat purity is measured as 24 times the purity by mass:
where
- X is the carat rating of the material,
- Mg is the mass of pure gold or platinum in the material, and
- Mm is the total mass of the material.
Therefore, 24-carat gold is fine (99.9% Au w/w), 18-carat gold is 75% gold, 12-carat gold is 50% gold etc.
The carat system is increasingly being complemented or superseded by the millesimal fineness system, in which the purity of precious metals is denoted by parts per thousand of pure metal in the alloy.
The most common carats used for gold in bullion, jewelry making and by goldsmiths are:
- 24-carat (millesimal fineness 999 or higher)
- 23-carat (millesimal fineness 958)
- 22-carat (millesimal fineness 916)
- 21-carat (millesimal fineness 875)
- 20-carat (millesimal fineness 833)
- 18-carat (millesimal fineness 750)
- 15-carat (millesimal fineness 625)
- 14-carat (millesimal fineness 585)
- 10-carat (millesimal fineness 417)
- 9-carat (millesimal fineness 375)
- 8-carat (millesimal fineness 333)
- 1-carat (millesimal fineness 042)
Derivation:
The word carat is derived from the Greek kerátion - “fruit of the carob”. Carob seeds were used as weights on precision scales because of their reputation for having a uniform weight. This was not the only reason. It is said that, in order to keep regional buyers and sellers of gold honest, potential customers could retrieve their own carob seeds on their way to the market, to check the tolerances of the seeds used by the merchant. If this precaution was not taken, the potential customers would be at the mercy of "2 sets of carob seeds". One set of "heavier" carob seeds would be used when buying from a customer (making the seller's gold appear to be less). Another, lighter set of carob seeds would be used when the merchant wanted to sell to a customer.
In the distant past, different countries each had their own carat, roughly equivalent to a carob seed. In the mid-16th century, the Karat was adopted as a measure of gold purity, roughly equivalent to the Roman siliqua (
of a golden solidus of Constantine I). As a measure of diamond weight, from 1575, the Greek measure was the equivalent of the Roman siliqua, which was 
of a golden solidus of Constantine, but was likely never used to measure the weight for gold.
of a golden solidus of Constantine I). As a measure of diamond weight, from 1575, the Greek measure was the equivalent of the Roman siliqua, which was of a golden solidus of Constantine, but was likely never used to measure the weight for gold.Terminology
22/22K - a quality mark indicating the purity of gold most popularly used in India. This purity was adapted and practiced by the big jewellers and was later passed to jewel smiths. The first 22 signifies the "Skin purity", the purity of the top layer of the gold jewelry, and the second 22 signifies that after melting purity of the gold jewellery will be 22-carat, or 91.67% of pure gold. This system is used to show consistency in the quality of the gold.
This practice was pioneered and introduced in the early mid-1980s by Nemichand Bamalwa & Sons of Kolkata, India, sparking a revolution in India, as it forced jewellers to indicate correctly the after-melting purity. Heightened consumer awareness made it a most sought-after stamp or quality mark.
This symbol or stamp can be found in Asian countries like India, Sri Lanka, Pakistan, Bangladesh, Nepal, Yemen, and Persian Gulf countries.
International caratages of gold jewellery| Region | Typical caratage (fineness) |
|---|---|
| Arabic countries, Far East (China, Hong Kong, Taiwan) | 24-carat "Chuk Kam" (99.0% min) |
| Arabic countries, Bangladesh, India, Pakistan, and Sri Lanka | 22-carat (91.6%) |
| Arabic countries in the Persian Gulf region | 21-carat (87.5%), 18-carat (75.0%) in most Egypt |
| Europe - Southern / Portugal | 19.2-carat (80.0%) |
| Europe - Southern / Mediterranean | 18-carat (75.0%) |
| Europe - Northern Germany etc. | 8- to 18-carat (33.3 - 75.0%) |
| Russia/former USSR | 9- (37.5%) and 14-carat/old 583 and new 585 проба (58.5%) |
| United Kingdom | 9-carat to 22 carat (37.5-91.6%) |
| United States | 10-carat to 18-karat (41.7-75%) |
Hallmark in India:
- Has acted as a safeguard to purchasers of gold and gold articles for centuries in various countries.
- Indicates that gold articles have been evaluated and tested at an official Assaying and Hallmarking Center and they have certified that the metal used conforms to the national/international standard of fineness/purity.
- Consists of BIS Standard Mark, Fineness Mark, Mark of Assaying and Hallmarking Center responsible for testing and hallmarking of jewellery, Mark of Certified Jeweller and year of Mark (denoted by a letter e.g. letter `A' for the year 2000 and letter `B' for the year 2001) as approved by BIS.
- Put on each article/ornament after ensuring its purity.
- Hallmarking of gold jewellery has been taken up on voluntary basis under BIS Act, 1986.
- Certification of purity of gold jewellery is done in accordance with Indian Standard Specification IS 1417 `Grades of gold and gold alloys, jewellery/artifacts Fineness and marking.
- BIS is operating this scheme with its network of Regional/Branch Offices all over the country.
- Assaying of gold and gold jewellery is being done as per IS 1418 `Method for assaying of gold in gold jewellery by BIS recognized Assaying and Hallmarking Centers.
Brief descriptions of the operation:
Jewellers desirous of hallmarking their gold jewellery will need to first become a `BIS Certified Jeweller. To get BIS certification, the jeweller has to apply to BIS and ensure homogeneity of batches of jewellery offered for Hallmarking by following a systematic quality control. The jewellers quality control system and conforming test reports forms the basis for Certification of Jeweller.
Objectives of the scheme:
- To protect consumer against victimization of irregular gold quality.
- To develop export competitiveness of gold jewellery industry and thus provide strong impetus for gold jewellery exports
- To develop gold based financial products that will help in mopping up of the vast dormant gold resources lying with the household sector.
- To develop India as a leading gold market center in the world commensurate with its status as the topmost consumer.
No comments:
Post a Comment