Product using the sericin, Tang chirimen. Photo: Kuwajima Kaoru

The refinement process to take away the sericin and impurities is called seiren. When 1 kg of cloth undergoes seiren of about 8 hours, it becomes 3/4 (750 g) of its original weight. Through this process, the fabric becomes softer and more lustrous as is characteristic of silk. Recently, products such as cosmetics and bath salts have been developed using the sericin extracted during the refinement process.