The art and science of jewellery manufacture
The ancient craft of making jewellery can be traced back to the days of early man, archaeological evidence of which dates back more than 100,000 years. Despite this long and varied history, new developments continue right through to the present day. Metal clay is one example of a new alternative way of making a piece of jewellery and advances in soldering techniques have enabled micro welders, with their very small flame, to fuse minute pieces in highly inaccessible cavities and places. The use of CAD (Computer Aided Design), 3-D printing and laser welding have also revolutionised the work of the master jeweller. The only drawback to some of the techniques outlined above is cost, a factor placing them out of the reach of many small independent workshops. However, as with all new technology, over time this limiting factor will recede as the price comes down.
(CAD – Computer Aided Design – has revolutionised jewellery manufacture)
Several jewellery making techniques – annealing, piercing and soldering – underpin every stage in the jewellery making process. As such they form the basis of every craftsman’s apprenticeship and they have to be mastered before more elaborate finishes can be produced. Jewellers start the creation of a piece with a precious or non precious metal. The precious metals are platinum, palladium, gold and silver. The non precious, or base metals, include copper, brass (an alloy of copper and zinc), zinc, tin, nickel, lead, titanium and niobium. The precious and non precious metals listed above are all non-ferrous (they do not contain iron) but the ferrous metals iron and stainless steel can also be used in jewellery making. The metals most conducive to jewellery making have the desirable characteristics of being reasonably strong, malleable, with a hardness achieved through working, a measurable density and a melting point that can be reached with a high-temperature torch.
(The precious metals: gold, platinum & palladium)
Platinum, the most expensive of the precious metals, has only been used extensively in jewellery making for around 100 years. It’s strength and resistance to oxidization (rusting), coupled with the beautiful appearance of its whitish-grey colour have made it a very practical and desirable metal. Pure platinum, with a pureness of 999, is rarely used for jewellery making purposes because it is too soft. Most platinum jewellery is 950 parts platinum to 50 parts copper. Other common alloys of platinum include 800 parts platinum, 200 parts iridium and 950 parts platinum and 50 parts gold. Different platinum alloys have different working properties and they have a very high soldering temperature, requiring the wearing of special eye protection. Tools used to work platinum must be kept separate from those used with other metals (or thoroughly cleaned with acid), as particles of other metals left on the surface can burn holes in the platinum when heated.
(Platinum, the hardest and most expensive jewellery metal)
Palladium is a relatively new metal and it has only recently been given its own mark of quality, which is 950. It is a bright white metal of lower density and specific gravity than platinum or white gold. Due to its ‘lightness’ palladium lends itself to the creations that would otherwise be a little heavy were they made in gold or platinum. Another of its advantages over white gold lies in the fact that it does not need plating and will consequently not fade over time. Typical alloys of palladium 950 include ruthenium and iridium, which are in the same group of metals as palladium. As with platinum, the melting point of palladium is rather high so special protective goggles are required to protect the craftsman’s eyes when soldering.
(An example of one of the Birmingham Assay Office Hallmarks)
Gold, for jewellery purposes, is available in 24, 22, 18, 10 and 9 carat. 24 carat, or pure gold, is rarely used other than for purely decorative work due to its softness. 22 carat (22 parts gold to 2 parts other metals – usually copper or silver) is usually buttery yellow in appearance although it may have a reddish tint if it is alloyed with copper. It is a popular metal with middle eastern craftsmen but it is too soft for some delicate pieces. 18 carat gold is 18 parts pure gold to 6 parts other metals, such as silver, copper and palladium. By varying the amount of these alloying metals, different colours can be achieved with the metal. 14, 10 and 9 carat gold tend to be used in cheaper jewellery pieces as the lower the carat, the less fine gold there is in the metal.
Gold can be produced in white, red, green or yellow. White gold is produced by alloying gold with silver and palladium and it has the useful qualities of being malleable and strong. It is usually rhodium plated, once it has been finished and polished, to give it a bright sheen. Red (or ‘Rose’) gold is produced by alloying more copper than silver to pure gold. Green gold is rarely used but it is malleable and has an aesthetically pleasing appearance. It is made by mixing gold with cadmium, copper and silver. Yellow gold is normally alloyed with copper and silver and it is highly malleable and easy to work with. It is the most common incarnation of gold used in jewellery manufacture. The origin and type of gold contained in a piece of jewellery can be determined by examination of the hallmark.
(Gold comes in a variety of colours)
Silver, as with gold, is too soft to create jewellery in its purest form, defined as 999.9 silver. In order to make the metal workable, it needs to alloyed with 75 parts copper to 925 parts silver to make what is known as standard silver. Britannia silver, used largely by silversmiths when making large objects, has slightly less copper at 958. After it is annealed and softened, silver is easily worked. Sterling silver is an alloy of silver containing 92.5% by weight of silver and 7.5% by weight of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925. Jewellery manufacture continues to evolve and adapt to advances in technology and techniques that have been honed over many centuries.