The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
1 troy ounce of four nines fine gold (999.9)
A 2019 American Silver Eagle bullion coin with a fineness of 999 (three nines fine), together with a Walking Liberty half dollar with a fineness of 900 (one nine fine); this latter alloy is also often referred to as 90% silver or coin silver.
Carob (Ceratonia siliqua) pod and seeds, origin of karat via Arabic qīrāṭ which itself comes from the Greek word for the seed kerátion
In chemistry and materials science, impurities are chemical substances inside a confined amount of liquid, gas, or solid. They differ from the chemical composition of the material or compound. Firstly, a pure chemical should appear in at least one chemical phase and can also be characterized by its phase diagram. Secondly, a pure chemical should prove to be homogeneous. The perfect pure chemical will pass all attempts to separate and purify it further. Thirdly, and here we focus on the common chemical definition, it should not contain any trace of any other kind of chemical species. In reality, there are no absolutely 100% pure chemical compounds, as there is always some small amount of contamination.
Three gems from the beryl family with different colors.
