Like diamonds, South Sea pearls also have grading systems to assess their quality. At Diamonds and Pearls Jewellery, we follow the Autore Five S grading approach to assist us in explaining the unique characteristics of your South Sea pearl.
According to Autore, the Five S’s are: Shine, Surface, Shape, Shade and Size.
As in all things, true beauty comes from within, so the virtue rated above all others in a South Sea pearl is its lustre and shine. Lustre is the result of light reflected from the pearl’s surface combined with its deep inner glow (iridescence).
South Sea pearls are made up of many fine layers of a crystal-like substance called nacre, comprising organic and inorganic materials secreted from within the living tissue of the oyster. The quality and thickness of nacre gives a pearl both its radiance and its deep glow. The combination of light reflecting on the pearl’s surface and light refracting between each layer of nacre within the pearl is what makes this gem unique.
Shine has the magic to minimise other imperfections and is considered the soul of the pearl.
There are five broad categories of lustre:
I Brilliant Lustre: producing a mirror reflection
II Excellent Lustre: producing a very clear reflection
III Good Lustre: producing a good reflection
IV Average Lustre: the reflection appears opaque
V Poor Lustre: producing very little reflection
There are two essential aspects to be considered when assessing the surface of a pearl: blemishes and grain.
The surface of a pearl is essentially its skin. Because South Sea pearls have layers of lustrous nacre built up over time, a flawless surface is extremely rare.
As pearls are a gift of nature from a living mollusc, the most beautiful and valuable pearls may still have slight imperfections which appear in the form of small blemishes. These naturally bestowed ‘beauty marks’ characterise each pearl as an individual creation.
The pearl grain refers to the composition of the pearl’s skin and its structure. The tighter the structure of the pearl, the less evident is its grain. The grain will appear as slight ripples on the pearl’s surface.
In cases where the grain is only just visible, it will give the pearl a slightly fractured appearance. As these fractures become larger and more evident, they will appear as “cracks” within the structure of the pearl.
South Sea pearls come in a variety of shapes, making them an incredibly difficult gem to classify without a professionally trained eye. A product of nature, each pearl is individual and unique.
The major categories of South Sea pearl shapes are; round, near round, drop, button, baroque and circle. With the exception of round and near round pearls, there is a variation of different types within each shape category. However, to simplify pearl shapes, some general principles can be applied.
- Round: Pearls are formed in oysters seeded with a spherical bead (nucleus) made from freshwater mussel shell. Only a small percentage of harvested pearls are perfectly round. As a broad principle, a pearl is considered round when the variation in its diameter is less than 2.5%. Therefore, a pearl measuring 10mm can have up to 0.25mm variance and a pearl measuring 20mm can have up to 0.50mm variance.
- Near Round: A pearl is classified near round rather than round when the variation in its diameter is roughly more than 2.5 %. This percentage may vary when there are lumps or slight variations to the pearl’s shape.
Near round pearls are ideal for jewellery and strand making as they appear round once set.
- Drop: There are several types of pearls that fall within the drop shape category. They include teardrop, oval and egg shaped pearls, as well as the more unusual semi-drop and cone shapes. While variations in the category can be quite dramatic, the one basic principle is the vertical axis of a drop pearl must always be longer than its horizontal axis. Short oval shaped pearls can be similar to near round pearls in appearance. The greater the difference in size between the vertical axis and the horizontal axis, the more unusual and rare the pearl is.
- Button: As with the drop category, buttons can also vary dramatically in appearance. However, in direct contrast to a drop pearl, the vertical axis of a button pearl must always be shorter than its horizontal axis. High Button pearls can be similar to near round pearls in appearance.
- Baroque: The baroque pearl is the most individual South Sea pearl produced by the Pinctada maxima oyster. Generally speaking, a baroque pearl is irregular or free form in shape. If the baroque pearl is relatively symmetrical, it can be used in a number of different ways in jewellery and strands. Occasionally, baroque pearls will have what are called ‘fish tails’. In some circumstances, one side of a baroque pearl will be symmetrical or round. These pearls are classified as semi-baroque.
- Circle – A pearl that has one or more parallel grooves etched around its circumference is called a ‘circle’. All shapes can be classified as circle pearls if these rings or grooves are present. The only exception is when a drop pearl has a ring around its apex, in which case the pearl is classified as a semi-drop and not a circle.
The species of oyster and the environment in which they grow are the main factors behind determining a pearl’s colour and complexion. South Sea pearls are highly coveted for their rich, varied colours.
Pearls from the Pinctada maxima oyster come in shades of white, ivory, silver, blue, yellow and rich gold. Pearls from the Pinctada margaritifera oyster (referred to as Tahitian or Black pearls) come in shades of aubergine, blue, green and grey, all with various hues.
Each pearl reflects colour in a different way – boldly on the surface or hinting at hues from within layers of nacre.
South Sea pearls are renowned for their large sizes. The Pinctada maxima oyster is the largest species of oyster capable of producing a pearl. South Sea pearls are measured in millimetres and commonly range from 9-20+mm, with the majority falling within a range of 10-17mm. Though extremely rare, the irregularly shaped baroque South Sea pearl can reach sizes of up to 40mm or more.