For Ryuichi Kumakura, a 70-year-old cut glass artisan, finding young workers eager to learn and preserve the traditional Japanese craft is the least of his troubles -- showing them how to engrave exquisite pieces of glassware with precision is what matters most.

Having a decent "business mind that evolves with the times" is vital also in the field of traditional crafts, said Kumakura, who began selling Edo Kiriko hand-cut glass directly to consumers about 30 years ago in a rare move back then for an industry that relied on a wholesale system while artisans themselves focused on production.

Edo Kiriko is a type of traditional cut glass originating in Edo, the former name of Tokyo, toward the end of the Edo period, which lasted from the early 17th to late 19th centuries. Kiriko means a faceted object in Japanese.

A multitude of decorative patterns is engraved on the surface of the glass using grindstones and other tools. With only rough outlines, artisans are able to carve detailed but accurate lines freehand.

For his "kometsunagi," or rice chain, pattern, Kumakura subtly varies the size of the life-size rice grains. It is hard to tell the difference, but herein lays the secret of the exquisite pattern.

"Engraving 1 millimeter off (the line where it should be) would kill my work," Kumakura said in a recent interview. "We're in a world where 0.1 millimeter matters a lot."

Kumakura's wine glasses with his original "kometsunagi" decorative pattern were selected by the government as gifts to world leaders at the Group of Eight summit in Hokkaido in 2008 and for other foreign dignitaries on other occasions.

Unlike many traditional craft workshops plagued by a shortage of successors, his workshop in Tokyo's Kameido is full of young men and women aspiring to inherit his techniques.

Kumakura dismisses the conventional wisdom offered by craftsmen that newcomers should "steal" seniors' techniques by carefully "watching" them.

"It's so outdated," said Kumakura, who holds an extra training session for his young staff every week after work to help them polish their trade. "Our studio's motto is accuracy and speed," he said.

The origin of Edo Kiriko has been traced back to 1834, when Kagaya Kyubei, who was working at a glassware store in Edo, made an engraving on a surface of glass with an emery grinder, according to the Edo Kiriko Cooperative Association.

Following Edo Kiriko, cut glass was also produced in Satsuma, now the southwestern Japan prefecture of Kagoshima, under the leadership of Shimazu Nariakira, a Satsuma Domain feudal lord.

Satsuma Kiriko soon gained a reputation for its quality but production came to a halt not long after the death of the lord in 1858 and the destruction of factories during the Anglo-Satsuma War in 1863, according to local Satsuma Kiriko makers.

The present style of Edo Kiriko was established after a group of Japanese craftsmen took lessons from a visiting English technician of cut glass in 1881.

While Satsuma Kiriko disappeared for over a century before local craftsmen revived production in the mid-1980s, Edo Kiriko survived in artisans' workshops in Tokyo. Edo Kiriko was designated by the government as an official traditional craft in 2002.

Today, around 90 Edo Kiriko craft workers still practice their art in workshops mostly located in Koto and nearby wards just to the east of central Tokyo, according to the industry's association.

While Kumakura's studio faces no shortage of young workers ready to carry on his art, the overall traditional crafts industry in Japan faces a shortage of successors.

The number of people engaged in industries designated by the government as traditional crafts fell to 64,889 in 2015, less than one-fourth of the level seen in 1979, according to the Association for the Promotion of Traditional Craft Industries.

Japan's 230 designated traditional crafts are mostly produced by individuals or small firms and given changing lifestyles and the influx of cheap imports, the overall industry is in a "critical situation" with regard to passing on traditional production skills to the next generation, the Ministry of Economy, Trade and Industry warns.

Indeed, customers' preferences have changed with the times, said Kumakura.

As more Japanese houses have no Japanese-style tatami room, which typically has a tokonoma display space, large flower vases and dishes for decoration purposes have seen demand drop, and instead practical items such as sake and wine glasses have become the vogue, he said.

Kumakura's family business, founded by his father Mokichi, has been manufacturing glassware for about 70 years.

He opened his own retail store, called Hanashyo, in the 1980s following the bankruptcy of a glass company to which he used to supply products.

Kumakura's products gradually built up a reputation through word of mouth, and the store's sales grew 2.5-fold over the past decade and most of the customers are repeaters.

The store helps him keep in touch with what customers want, he says. Small sake glasses sold in various colors at his shop cost from around 9,000 yen ($79) to 120,000 yen.

His studio now employs 10 craftsmen and women, mostly in their 20s and 30s.

One staff member, Kazuki Yusa, 27, said he had trouble just figuring out how to blink and keep his eyes focused at the beginning of his glass-carving career.

"We have to watch the center of the blade (of a motor-powered wheel) through glass but I couldn't see it at all in the beginning," he said. "I forgot to blink as I was concentrating on (the center) so much."

Kumakura's studio uses its own engraving equipment and polishing method for a brilliant finish. He has not hesitated to collaborate with other traditional artisans, jumping at the chance to work with an Arita Yaki ceramics maker in Saga Prefecture, southwestern Japan, to create a lamp using an Edo Kiriko shade and ceramic lamp base.

"We make unique patterns and products using our original techniques. I believe they aren't something that can be copied easily," he said.