Appraising Gemstones

When you are first presented with a tray of gemstones it is easy to feel dazzled and slightly overwhelmed, and to forget to look at the stones in detail. It is not difficult to miss basic faults, only to realize a couple of days later that the gemstone you purchased is not quite as good as you thought.

First you need to know that you are looking at the real thing – that the sapphire really is a sapphire and not a fake. Other than going to the effort of taking the stone for testing at a laboratory, you need to choose a reputable dealer. Preferably this will be someone who is recommended by other dealers, who knows the history of the gemstones he or she is selling and who will offer you good trade prices. It’s worth remembering that within the gem trade, reputation is everything – dealers who get a bad name for deceiving a customer don’t survive in the business for long.

Touch Them
Gemstones look lovely in their presentation cases, but you should never buy a stone without taking it out of its box or bag first. Boxes can hide flaws and cracks, alter the colour of the stone and disguise poor cutting. A good dealer will take the gemstone out for viewing without being asked. Many faults, such as symmetry, quality of colour, inclusions and surface damage, can be seen with the naked eye as long as there is a good light source.

The light should come from above or behind you, so it shines down through the stone. Some store lighting is designed to make a gemstone look intense and dazzling; don’t be afraid to ask to see the stone in daylight. A piece of white paper will also help you to judge colour properly. Hold the stone against the white background and look at it from the top and the sides, then turn the stone upside down to check for colour zoning.

If you are unpracticed with tweezers then don’t use them; you can lift the stone up in a tray and rotate it through 360 degrees. Balancing the gemstone on the back of your hand, with the culet sitting between your fingers, will help you to identify shallow stones and evaluate size in relation to your hand. Feel free to use a loupe (jewelry magnifier), but practice before visiting the gem store. It is useful to take along a small penlight, to reveal any cracks in cabochons, and a lint-free cloth to remove grease.

Look at gemstones when you are fresh; don’t view them at night or if you’ve been working all day. Comparison is the best means of appraisal – the more stones you look at; the quicker you will separate good from bad. Get to know the comparative carat prices of different materials. It may seem obvious, but double-check the name of the gemstone with the dealer. Misnomers are still used; for instance, citrine often gets called topaz. Finally, take account of your gut feelings – does the stone excite you? If a gemstone seems too good to be true, it probably is!

As with faceted stones, rarity, colour and optical effects are the main indicators of value. A symmetrical outline, flat, solid base and good finish are also important. The degree of clarity is less crucial because cabochons are typically cut from lower-grade material, but stability is important as a cracked stone might break during setting. Check for cracks by running your fingernail over the surface and shining a penlight through the stone.

Surface finish, drilling, symmetry and evenness of cutting are the prime indicators of quality in beads. Cracks, chips, wonky drilling and poor polishing are common faults.

What to look for in a gemstone
Gemstones can be rare for a variety of reasons – the type of gemstone, the origin, the colour or the size. However, rarity doesn’t automatically mean that a stone is valuable as it still needs to be assessed on other criteria. Check to see if the stone has a certificate.

In general, treatment, whether it is heating, irradiation, staining, dyeing, fracture filling or stabilization, devalues a gemstone. Heat treatment is more acceptable than the others as it doesn’t affect the future wearability of the stone. Some processes, such as irradiation, fracture filling and beryllium or diffusion treatment, are not permanent.

This is the most important aspect of a colored gemstone, worth at least half of the total value of the stone. The finer a gemstone’s colour, the less impact cutting, clarity and weight will have on the value. If the colour of a stone is poor, brilliance will be an important factor. The closer the colour comes to a pure hue (spectral colour), the rarer and more valuable the stone. Intensity or saturation of colour is also an indicator of quality and highly desirable, but will be diminished by irregular colour distribution and the presence of grey tones. View a stone in both artificial light and daylight. Some gemstones, such as kunzite and amethyst, can fade naturally over time and should not be worn in direct sunlight. The style of setting can affect the colour of a gem; rub-over collets can make dark stones appear even darker or intensify the colour of pale stones.

Is the gemstone suitable for your design? Will it survive the intended wear and tear?

The quality of an optical effect such as asterism or colour change is as important as colour o clarity, and will affect the value of the stone.

Clarity is worth approximately 20 to 30 per cent of the total value of a gemstone. Some inclusions acceptable, as they can prove a stone’s identity and origin and will not affect the value. However, as a rule heavily included faceted stones are not as much as “clean” stones, because internal flaws can spoil a gemstone’s appearance and undermine its stability.

The cut accounts for 10 to 20 per cent of total value. It is less critical than colour and clarity because it can be changed. Gems that are cut very deep will be overweight (and therefore expensive) for their size and dull. A shallow stone that has a large spread might look showy, but will have little “life” and could break during setting. It may be advisable to recut a good stone to better proportions, despite the loss of weight and size.

Finish accounts for about 10 per cent of total value. It is reasonable to ask the dealer to polish out any abrasions, scratches or chips as a condition of the sale.

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