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Gemstones

Articles from GEMSET JEWELLERY (300 Articles)












Repair tips for gem-set jewellery

An important skill for any bench jeweller is knowing how to minimise the risk of damage when working with gem-set jewellery. IAN DUN offers advice for managing gemstones in the workshop.

Bench jewellers are often required to work on gem-set jewellery. This work could be relatively straightforward or quite complex depending on the type of gemstone(s) present. With the right preparation, highly durable gemstones can be left in place for many procedures, while gemstones with lower durability and resistance to heat require removal or extensive protection before repair work can commence.

Here are some examples of how commonly encountered gemstones should be handled.

Diamonds are frequently left in place for repair and basic procedures are required to minimise the risk of damage. It is common for worn settings and claws to be restored and diamond’s exceptional combination of hardness and heat conductivity allow it to tolerate the temperatures these procedures generate. For flame-based soldering or re-tipping, cleanliness and a protective coating is necessary to protect the diamond’s surface from oxygen, which can burn or fire-stain the stone. If setting or resetting diamonds, excessive pressure on the cleavage planes or at the girdle may also cause damage.

Sapphire, ruby and most of the corundum family are also blessed with high levels of durability and may be subjected to similar processes but with lower levels of resistance to heat and pressure. It is important to ensure that members of the sapphire family are free from inclusions or easily replaceable if direct heat is applied. It is common for sapphire to have internal features that may expand under heat, especially if not heat-treated; however, temperatures commonly applied in the heat-treatment process are much higher than those used in workshops, so heat-treated sapphires have slightly lower levels of risk.

Similar protective procedures are applied to sapphires as with diamonds and only certain types of flux are suitable. Pressure, thermal and mechanical shock should be avoided.

Gemstones crystallised in lower-heat environments such as the beryl, quartz, tourmaline, topaz, garnet and feldspar families are usually resistant to moderate heat, acids and gentle abrasives. If gemstones are of high clarity and without pre-existing damage, they should be protected sufficiently for jewellery resizes and basic modifications.

When applying heat to pieces where high temperatures may cause damage, it is common to immerse items in water or cover with a protective paste. In metals with lower heat conductivity like high-carat gold and platinum, a solder repair may be completed without the metal transferring much heat to the gemstone. For heavy pieces, especially silver items, great care is needed to offset the conduct of high levels of heat away from the repair site. It is now possible to apply heat in closer proximity to these gemstones using laser and pulse-arc welders. Avoid direct heat application if welding adjacent to these gemstones as their low thermal conductivity can result in localised fracturing.

Satisfactory outcomes can be achieved when gemstones are accurately identified as suitable for the procedure and the necessary steps are undertaken with care and skill. However, potential for damage exists in all cases and there are situations where removal of gemstones and extensive protective measures or even refusing to undertake
the work is prudent.












ABOUT THE AUTHOR
Ian Dun

Ian Dun FGAA, is a GAA and Gold & Silversmiths Guild of Australia fellow. He has more than 30 years’ experience as a gemmologist and manufacturing jeweller. For more information on gemstone best practice, visit: gem.org.au









Saturday, 16 December, 2017 01:13am
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