About Precious Metals
This most famous of precious metals has been highly sought after and valued throughout human history not only because of its rarity and beauty, but also because of its usefullness and that it is often found highly pure in content. Gold is very malleable (easy to work with) and durable because it does not corrode or tarnish. Its malleability can be realised if we think of how just one ounce od gold can be beaten into a flat sheet of gold leaf measuring 17 square metres.
As for its durability, we only have to consider all the historical relics such as ancient Egyptian artefacts which have survived intact for thousands of years. Considering this then, one begins to comprehend just how ancient and historically important the craft of goldsmithing is.
Pure gold is very soft and therefore liable to damage. For this reason, most gold jewellery is made of gold alloys. The content of gold alloys consists of gold and other metals. The gold content of jewellery is measured in carats (expressed fractionally as 24ths). For example, 24 carat jewellery is pure gold, while 9 carat gold has a gold content of 9/24ths, or just over one third.
Though not as highly valued as gold, this soft and lustrous white metal has a proud history dating back thousands of years. Ornamental and decorative siverware has been unearthed in royal tombs dating back to 4000 BC. Although much harder than gold, silver can be easily worked and beaten into silver leaf for decorative use. And just like gold it is long lasting and hard-wearing.
Silver has been used in jewellery and coinage throughout the ages in the form of a silver alloy. The fineness of silver items is measured as a proportion of the silver content. For instance, Sterling silver has a fineness of 925, which is to say that the silver content amounts to 92.5% of the piece. The other metal content of silver alloys used in jewellery is usually copper. Most silver jewellery has a fineness rating of 800, so there is 80% silver content and 20% copper in most silver jewellery.
High silver content is also evident in white gold. The gold content of white gold usually amounts to just over half, with silver amounting to one quarter of the content.
Although artefacts containing platinum have been found dating back to the times of the ancient Egyptians, it is thought that they were unaware of this precious metal being present in the mainly gold pieces it has been found in. The first discoveries which identify Platinum as a distinct precious metal occurred in 16th century Columbia. Indeed, the name Platinum dates from this time, when Spanish invaders noted its resemblance to silver ; the word platinum coming from the Spanish, 'platina del Pinta'.
The demand for platinum in jewellery has greatly increased in recent times, with particularly high demand in Japan. Most of the world's platinum comes from the Transvaal area of South Africa and Russia.
TThe history of mankind's use of bronze stratches way back to 3000 BC. Bronze is often an alloy made up of the metals copper and tin, although in recent times bronze has also been made using aluminium, manganese or zinc instead of tin.
Being very hard and durable yet easy to cast, bronze has been widely used throughout history for coinage, tools and weaponry. Iron hjas taken the place of bronze in many uses over the centuries because it is more widely available, reather than it being significantly better or more suited to its uses.
The content and value of precious metals is determined by processes of chemical analysis called assaying. The history and formulation of the processes involved is rooted in the work of ancient alchemists and goldsmiths who would subject base metals to heat.
Assaying by fire is still the most economical methos of assaying precious metals, even more so than modern methods such as spectrographic analysis because of the amounts of the metals needed to carry out the tests. The fire assaying method consists of 6 steps :
1. Sampling. A representative sample is taken.
2. Fusion. The sample is then melted along with flexes and other agents to collect elements of precious metals in droplets of lead. These are then cooled to produce a 'lead button'.
3. Coppelation. The 'lead button' is then melted and the impurities are oxidised. Beads of precious metals then form.
4. Weighing. Beads of gold and silver are then weighed to determine their gold and silver content. Platinum is present in quantities to small to weigh however.
5. Parting. Each bead is then trated to dissolve out the silver content.
6. Weighing. Finally, the remianing gold content is weighed andthis mesurement is subtracted from the gold-silver bead weight previously measured. This calculation then gives us the weight of the silver content.