Gold and Silver Purity

Gold and silver in their pure natural state are soft and flexible, and therefore are mixed with other metals that harden them. The other metal alloys with which the gold and silver are mixed are called "additives" – copper, silver, zinc, nickel, palladium, and others.
In precious metal alloys, the purity level is the percentage of the precious metal within the alloy mass. Purity is measured in one-thousandths. A pure alloy (99.99%) is described as "4 nines".‎ The level of purity also determines the price of the alloy.

Gold Purity
The percentage of pure gold is noted in karats, with one karat equal to 4.1666%.
The gold purity levels permitted for trade in Israel are:
24 karat – contains 99.99% pure gold (4.1666 times 24 = 99.99); hence its name: four nines fine.
22 karat – contains 91.6% pure gold (4.1666 times 22 = 91.6) and 8.4% other metals.
21 karat – contains 87.5% pure gold (4.1666 times 21 = 87.5) and 12.5% other metals.
18 karat – 75% pure gold.
14 karat – 58.5% pure gold.
9 karat – 37.5% pure gold.
Products with a purity level of less than 9 karats gold are not considered gold products according to Israeli law.
The other metals the pure gold is mixed with are what determines the gold's hue. Pure gold (24 karat) is yellow – in order to maintain its yellow color, it's mixed with palladium, copper and silver. Mixing with copper, which has a reddish tint, creates "red gold", while mixing with pale metals such as nickel or platinum creates "white gold".

Silver Purity
Karats are not used in silver. 999 silver – pure silver – is not used in jewelry in which minimal hardness is required. 925 silver – also known as sterling silver – is the most common alloy used in the manufacture of silver jewelry and other fine silver items.
The silver purity levels generally accepted in Israel are:
99.9% purity – 999 thousandths.
92.5% purity – 925 thousandths.
83.5% purity – 835 thousandths.
80% purity – 800 thousandths.

Purity Verification and Marking
According to Israeli law, every gold product must undergo a process of verifying its purity in order to protect consumers from fakes, and there is an Israeli standard for marking gold products (IS 299) according to which only gold products meeting the standard's requirements may be imported, manufactured and marketed.
The Standards Institution of Israel (SII) checks the manufacturer's/importer's mark and the purity mark. After the examination, the institution's certification mark is stamped, proving that the purity mark imprinted on the product is in fact correct.
Gold products that do not feature these three marks may not be marketed.
Products weighing less than 2 grams do not need to be marked, although the manufacturer is still obliged to bring the jewelry to the SII for verification.
There is no obligation to mark the purity level on silver jewelry, and marking is voluntary.

The certification mark for gold is a "David's Harp" and for silver is a "Pomegranate".