Lighting your display cabinet

Light makes or breaks a collection

A badly lit mineral collection looks dull, however fine the pieces. Well lit, it becomes a spectacle. And since each family of stones reacts differently, there is no universal lighting: you must choose, or better, combine.

Colour temperature, stone by stone

For diamonds and colourless stones, favour cool white LED (5000 to 6500 kelvin): it awakens the fire — that dispersion of light into coloured flashes — and maximises brilliance.

For gold, amber, citrine, carnelian and all warm tones, warm white light (2700 to 3000 K) sets the golds alight and gives them a honeyed depth. Under cool light these stones look washed out.

For emeralds, sapphires and blue or green stones, neutral white (around 4000 K) offers the best balance — neither yellowing nor artificial blueing.

CRI: the number nobody checks

This is the most important parameter, and the most ignored. The colour rendering index (CRI), printed on lamp packaging, measures how faithfully a light reproduces colours, on a scale up to 100. Insist on a CRI above 90. Below that, your stones are lying: a CRI 70 bulb can make a magnificent emerald look grey.

The pitfalls to avoid

Avoid halogens: they run extremely hot, which is dangerous for opals (which hold up to 20% water and can craze), for amber, and for any stone sensitive to thermal shock.

Avoid too, prolonged exposure to sunlight behind glass: amethyst, rose quartz, citrine, kunzite and topaz fade irreversibly under ultraviolet light. A cabinet by a south-facing window is a trap.

Finally, keep a small dark corner for your fluorescent stones with a UV lamp: fluorite, calcite, willemite, scheelite. It is the showstopper of any collection.