Lake Biwa, in Shiga Prefecture of central Honshu, is the largest freshwater lake in Japan and one of the world's oldest, with a geological history extending some four million years. From a gem-and-jewellery perspective Lake Biwa is significant as the principal locus of mid-twentieth-century freshwater pearl culture, and as the body of water from which the term 'Biwa pearl' entered the international jewellery trade. The cultured freshwater pearls of Lake Biwa, produced from approximately 1935 through the early 1980s, set the technical and aesthetic standards against which the later Chinese freshwater pearl industry was measured, and 'Biwa' became, for a period, a generic descriptor in much of the trade for any non-bead-nucleated freshwater cultured pearl.

The freshwater mussel

The mussel cultured for pearl production in Lake Biwa was Hyriopsis schlegelii, a freshwater bivalve native to the lake. The species produces a relatively large nacreous shell and was found, through the experimental work of the Mikimoto and successor laboratories in the early twentieth century, to accept tissue grafts and produce well-formed pearls without bead nuclei. The technique, refined from approximately 1935 onward, involved the surgical insertion of small pieces of mantle tissue from a donor mussel into the body cavity of the host, with each mussel typically receiving multiple grafts and producing multiple pearls per harvest. The growing time was generally three to five years, longer than the corresponding cycle for Akoya saltwater pearls.

Production characteristics

Biwa freshwater pearls are characterised by their non-bead-nucleated structure, which means that the entire pearl is composed of nacre laid down concentrically around the original tissue graft. The shapes were typically irregular: rice-grain, oval, button and baroque, with rounder shapes being uncommon. Sizes ranged broadly from about three to twelve millimetres. Body colours included white, cream, pink, peach, lavender and bronze, with the natural colours strongly preferred over dyed material in the better part of the trade. The classic Biwa pearl was lustrous, with thick nacre, displayed strong orient, and showed the slightly irregular shape of a tissue-nucleated freshwater. Strands of well-matched Biwa pearls became a standard offering in the international jewellery trade through the 1950s, 1960s and 1970s.

Decline of the fishery

The Biwa pearl industry declined sharply through the 1970s and 1980s for a combination of reasons. Industrial pollution and eutrophication of the lake, a consequence of the rapid economic growth of post-war Japan, substantially impaired water quality. Mussel diseases compounded the difficulty. By the late 1980s commercial production had effectively ceased, although small-scale experimental work has continued. At the same time, Chinese freshwater pearl operations on the lakes and rivers of southern China, using the mussel Hyriopsis cumingii (and later hybrids), grew rapidly and replaced Japanese freshwater production at scale by the 1990s. Modern Chinese freshwater pearl production now dominates the global freshwater pearl market by several orders of magnitude over historical Japanese production.

The 'Biwa pearl' trade term

The term 'Biwa pearl' was used in the international jewellery trade through the 1980s and into the 1990s as a generic descriptor for tissue-nucleated freshwater cultured pearls, including Chinese material that had no connection with Lake Biwa. This usage was challenged on origin-grounds and eventually fell out of favour in favour of more accurate 'Chinese freshwater' or 'freshwater cultured pearl' descriptors. The CIBJO Pearl Book and FTC guidelines now require accurate origin disclosure, and a pearl marketed as 'Biwa' should, properly, be one cultivated in Lake Biwa itself. Most contemporary 'Biwa-style' freshwater pearls in the market are correctly described as freshwater cultured pearls of unspecified or Chinese origin.

Position in the modern market

Authentic vintage Biwa pearls, particularly well-matched strands of the post-war period, retain a defined place in the antique and estate market and are valued for their distinctive lustre, colour and historical significance. Modern Chinese freshwater pearls, while produced in greater volume and at lower cost, have substantially closed the technical gap, and contemporary all-nacre Edison pearls and other premium Chinese material can rival or exceed historical Biwa material in size and roundness. For the working jeweller and historian, Lake Biwa remains the founding locus of commercial freshwater pearl culture, even as the industry has moved across the East China Sea to its modern centre.