Silver - The Relationship between Purity, Carats and Fineness


Silver is considered to be a soft, malleable metal available with a characteristic sheen. It has the highest electrical and thermal conductivities of all metals. It is usually found uncombined, or in the arsenide or sulfide ores from which it can be recovered as a cyanide complex which is consequently reduced to the metal, in aqueous solution, by using zinc.

The pure metal is stable to oxygen and water but is attacked in air by sulfur bearing compounds in order to form the characteristic black layer of silver sulfide. It is soluble in nitric and sulfuric acids.

Some silver salts are sensitive to light (example, AgI, AgBr and AgCl) and are of ultimate importance to photography. Other industries and applications in which silver is used include the electrical industry (example, in the manufacture of contacts), the manufacture of jewelry (both as a constituent of different alloys and as the pure metal) and for the silvering of glass.

The purity or fineness of silver alloys is now described using the millesimal system in most countries. This system uses a number to represent the purity of the alloy. The number described purity in parts per thousand.

Previous to the millesimal system, the fineness of silver was expressed in carats. While the fineness of silver alloys must be stamped or hallmarked into pieces, the millesimal value is generally compulsory and the carat value now optional.

Table 1. Some of the most common fineness denominations used.

Fineness Common Name Purity (wt.%)
999 Fine or pure silver 99.9
958 Brittania 95.8
925 Sterling silver 92.5
800 Jewellery silver 80


Pure silver is typically very soft and malleable, hence it is commonly alloyed to increase its hardness and durability for applications such as jewellery. It is typically alloyed with copper in this instance, with sterling silver being one of the most popular alloys, containing 7.5% copper. Copper is used as it is a hardening agent and does not discolour the silver.



  1. Emma R Emma R United States says:

    How do you test for Jewellery Silver?  I'm assuming it would not pass the acid test for sterling that is found in testing kits.
    Thank you.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.