As every Chinese schoolchild knows, pen, ink, paper and inkstone are the ancient scholar's "four treasures of the study." (Photos: Shi Jiamin; Compiled by Chen Xirui)

There is a fifth: grinding and dyeing ink with water to create an ink paste.

The brothers Zhang are heirs to this intangible cultural heritage.

Zhang Weiguo and Weizhong have refined the traditional materials, ingredients and production processes at their workshop in the Jinxian county town of Wengang, Nanchang city of Jiangxi Province.

They sell their specialist ink paste products to painters and calligraphers across China, Singapore, South Korea and Japan.