Gold has been used to make jewellery for thousands of years, because of its rarity, its beauty, resistance to tarnishing, and unique properties allowing it to be hammered, twisted, melted and cast into any shape. As a pure metal, gold is too soft for practical use, and it is therefore alloyed with a variety of other metals such as silver and copper, to create a greater hardness and strength.
Gold is available in various standards called "carats", (abbreviated to "ct") which signify the purity of the metal. A carat represents "a one-twenty fourth part". For example, in 18ct, the purity of the gold is 18/24ths pure (i.e. 75% pure gold), the balance being various alloys added for additional strength.
9ct = 9/24th purity = 37.5% gold (A UK standard generally used in lower quality jewellery)
18ct = 18/24th purity = 75% gold (The International Standard used in high quality jewellery)
14ct = 14/24th purity = 58.5% gold (A Far East and US standard)
15ct = 15/24th purity = 62.5% gold (A defunct UK standard used until 1936)
22ct = 22/24th purity = 91.6% gold (In the past frequently used for wedding bands)
24ct = 24/24ts purity = 100% gold (Very soft, used principally for gold leaf decoration)
Cellini uses 18 carat gold, the International Standard, in its designs, as it provides the perfect combination of colour, high strength, and resistance to tarnishing.