The Six Forms of Freshwater Pearl
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Most people hold a single image of a pearl: round, white, matched to its neighbour. That pearl is real. It is also one outcome among several — the one the market has spent a century selecting for.
Set six freshwater pearls beside each other and the differences are not subtle. They are differences of shape, of surface, and of how light leaves them.
Six forms recur often enough to be worth naming. Other taxonomies divide them differently, and the boundary between some of them is genuinely unsettled — a point this article returns to.
Baroque
Irregular, without a plane of symmetry. No two are alike, and the difference between two baroque pearls is not a matter of degree; they are different shapes.
Under a light, a baroque surface does not produce a single highlight. It produces several, at different depths, moving independently as the pearl turns.
In the collection: the Aria, Athena, Celeste, Elara, Luna, Odessa and Stella.
Keshi
A keshi pearl has no bead at its centre — nacre from surface to core.
With no bead to determine the shape, keshi forms are the least predictable of the six. They tend to be flattened, folded or petal-like, and their lustre is often the sharpest in a mixed strand.
In the collection: the Flora Petal Pendant, Flora Keshi Bracelet, Flora Strand and Flora Ring.
Biwa
Elongated and flattened, longer than wide.
The name is geographical in origin — Lake Biwa in Japan, where freshwater cultivation was established — and now describes the form rather than the source. Most pearls sold as biwa today are not from that lake. Used here, the word means the shape.
That looseness is worth knowing before you buy. Across the trade, form names are applied with real variation: the same word can describe a shape in one place and stand as a category in another, and pearls of very different sizes are sold under it. A form name is where a question starts, not where it ends. What settles it is the outline in front of you — longer than wide, or not.
In the collection: the Aurelia.
Coin
Flattened into a disc, round or nearly round in outline, with two broad faces.
In light, a coin pearl behaves differently from a baroque one. The broad face pools light rather than scattering it, so coin forms read clearly at a distance, where irregular forms read as texture.
In the collection: the Portia and the Roman Holiday.
Rice
Small, oval, slightly elongated. The most regular of the six without being round.
Rice forms occur in narrow size ranges within a single strand, and they are the only form here that can be strung with something approaching rhythm.
In the collection: the Lyra.
Seed and nugget
Small, irregular, and — in these pieces — flattened and asymmetric rather than rounded.
This is the least settled name of the six. A small pearl that is nacre throughout and a small irregular pearl are difficult to tell apart once strung, and whether these are one form or two is not resolved here.
In the collection: the Vienna, and the smaller pearls of the Seraphina.
What the forms have in common
They do not repeat. The Vienna's strand carries no regular pitch. Its pearls sit at irregular intervals because they are irregular sizes, and that is a property of the material rather than of the stringing.
Variation within a pair is normal. In the Aria, the hoops of a pair are consistent mirror-images while the two pearls are not identical in outline. Matching was constrained by what the material offered.
Why the forms occur
A pearl is a deposit. A mollusc lays nacre — layers of aragonite bound with conchiolin — around whatever occupies its mantle tissue, and the shape of the finished pearl is the shape of that deposition. Deposition is not constrained to a sphere.
In cultured freshwater production, the usual practice is to graft a small piece of mantle tissue into a host mussel. The tissue forms a sac, and the sac secretes nacre. There is generally no bead at the centre, which is why freshwater pearls are typically nacre for most or all of their volume — a different construction from bead-nucleated saltwater pearls, where nacre is a coating over a shell bead.
That single difference accounts for most of what you see. A sphere is straightforward to produce when there is a sphere at the centre to copy. Without one, the sac grows as its position, surroundings and duration allow, and the pearl records that growth.
- Keshi occur when a graft produces nacre without a nucleus establishing itself, giving nacre throughout and an unpredictable shape.
- Baroque forms arise when deposition proceeds unevenly around the sac.
- Coin and biwa forms are associated with flattened or elongated growth, in some production encouraged by the shape of the graft.
- Rice and seed forms are small, and small pearls have had less growth time in which to accumulate irregularity.
These mechanisms come from the general literature on pearl formation. They describe how the forms arise in freshwater culture as a whole. They are not a cultivation record for any individual pearl, and no such record accompanies these pieces.
Form and the grading standard
Conventional grading rewards roundness, surface cleanliness, matching, and uniformity of size within a strand. A round pearl with an unblemished surface, closely matched to its neighbours, sits at the top of that scale.
That scale is coherent. It measures real properties, consistently, and it lets two strands from different sources be compared. There is nothing wrong with it.
It answers a different question from this one. Grading assesses how closely a pearl approaches a standard; a taxonomy of forms describes what the pearl is. A keshi graded against roundness scores badly by definition — not for being a poor pearl, but for not attempting to be a round one.
The practical consequence is that these forms were historically the by-product of a system optimised for one of them. Irregular pearls were what remained after the round ones had been selected out.
One thing worth stating plainly. Treatments that move pearls toward the graded standard — bleaching, dyeing, polishing and others — are used widely across the industry. These pieces are not sold with treatment documentation, and no claim is made here about what has or has not been applied to them.
What it means for choosing one
You can name what you have. A form is a description that holds up under examination, not a marketing category. Knowing that the pearl at your throat is a coin rather than a baroque is the difference between owning an object and owning a specific one.
Two pieces of the same form will not match. A second Flora will differ from the first. That is not a defect or a substitution; it follows directly from the formation. No bead at the centre means no template, and no template means no repetition. Matching cannot be promised without misrepresenting the material.
Form decides how a piece reads across a room. A broad flat face — coin, or the flattened wafers of the Aurelia — pools light and stays legible at distance. Irregular forms scatter light into several small highlights and read as texture, resolving into individual pearls only close up. Neither is better. They are different decisions about where the piece does its work.
Form is worth considering in care. Surfaces that are folded, ridged or deeply irregular hold more in their recesses than smooth ones do.
None of these forms can be made uniform without ceasing to be what it is. Uniformity requires a template, a template requires a nucleus, and these forms are, for the most part, what happens in a nucleus's absence.
A note on this article. An earlier version described the Aurelia's pearls as narrow batons. That was wrong — they are flat, overlapping wafers — and the description was corrected in July 2026. Corrections here are made openly rather than silently.