How to recognise a quality pearl

Introduction

Recognising the quality of a pearl is the first step towards choosing a jewel meant to last. The pearl is organic matter, grown inside a living mollusc: every specimen has characteristics of its own, and it is judged by observing several factors together.

What follows rests on gemmological criteria shared internationally and on the experience gathered in selecting and working pearls in fine jewellery.

For a complete view of the origin and of the different types of pearls, see A guide to pearls.

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Lustre

Lustre is the light the surface of the pearl sends back: it tells how far the gem behaves like a mirror. On a pearl of intense lustre the reflection of a window stays small and sharp-edged. Where the lustre is weak, that reflection widens and fades. It is one of the most important indicators of quality.

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Orient

Orient is a property distinct from lustre, and it is to be observed on its own. It is the iridescence that surfaces from beneath: the play of colours that moves across the pearl as it is tilted. It arises from the exceedingly thin layers of aragonite that make up the nacre. Light passes through them, is sent back by each of them and splits apart, as happens on the film of a soap bubble. In gemmological classification orient belongs to colour, alongside body colour and overtone. In short: lustre is the light that returns from the surface, orient is the light that returns from within.

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The surface

The surface of a pearl almost always carries small natural characteristics: growth lines, minute pits, slight bumps. They formed during the growth of the layers, and they are the proof of an authentic pearl. What counts is the number, the depth and the position: a mark on the side that rests against the skin weighs less than one at the centre of the pearl. The more continuous and even the surface appears, the greater the value of the gem.

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The shape

Shape bears on both appearance and value. Perfectly round pearls are the rarest. Irregular shapes have equal standing, though, and contemporary jewellery uses them gladly: the best known is the baroque, which denotes a shape and runs across every type of pearl. In a strand, shape is judged on the whole: pearls that resemble one another, matched with patience, are worth more than the same pearls gathered at random.

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The colour

The colour of a pearl is the one produced by the mollusc that made it. It is read in two stages: along the circumference one observes the body colour — white, cream, pink, purple, gold, grey, black — and at the centre the overtone, which may shift towards rosé, green or silver. A quality pearl shows a harmonious, even colour. The rarer a hue is in nature, the more it is worth.

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The size

Size is measured in millimetres, with precision callipers, and it bears on rarity and on value. It remains one factor among the others, however: a smaller pearl of high quality may be preferable to a larger one with lesser characteristics.

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Judging the whole

The quality of a pearl arises from the balance between all the factors. Lustre, orient, surface, shape, colour and size are to be considered together: it is their overall harmony that determines the value of the gem.

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Further reading

The complete guide to the seven factors by which a pearl is read, and to the method by which MIMÍ applies them, is found in How a pearl is judged. To understand the differences between the various types, see Types of pearls: differences and characteristics. Further technical information is gathered in A guide to pearls.