Black diamond calf
RARE CRAFTSMANSHIP FROM HIMEJI
At Jean Rousseau, we are particularly attentive to materials shaped through authentic craftsmanship, where leather is worked with patience and precision. In this spirit, we are introducing into our collections Black Diamond calf, known in Japan as Himeji Kurozan (姫路黒桟革), a material whose history and manufacturing technique rank among the most distinctive in Japanese leathercraft. It is produced from the hides of Japanese black-haired bovines, a lineage often associated with Japanese Black Wagyu.
A Longstanding Heritage Rooted in Himeji
Himeji, in Japan’s Hyōgo Prefecture, has been renowned for its leatherworking expertise for several centuries. This local tradition is built on precise tanning methods and the ability of craftsmen to create distinctive finishes suited to demanding uses.
Historically, Himeji Kurozan was used to produce protective equipment, particularly during the Sengoku period. Artisans crafted components intended to reinforce sections of armor worn by samurai. Its dense structure, robust tanning, and lacquered finish offered excellent resistance to friction and impact, making it well-suited to the military needs of the time.
This expertise later extended into modern martial arts, where the leather is still used for certain kendo protections, including parts of the bōgu.
Over time, this age-old know-how has evolved toward more contemporary applications, while preserving the technical mastery that defines it.
A Unique Manufacturing Process
Today, Black Diamond calf is still produced exclusively in Himeji. The Japanese calf leather is first tanned using traditional methods, then prepared in a way that highlights its dense, slightly raised texture.
This surface forms the foundation of the technique that truly defines this material: the manual application of successive layers of urushi, a traditional Japanese plant-based lacquer.
Each layer is applied in an extremely thin coat over the natural grain of the leather, left to dry, and then covered by the next. The process requires great precision and continuous control of the material.
As the layers build up, the surface gains depth and develops its characteristic sheen. The black becomes more intense, and the texture reflects light with clarity and control, creating the dense, almost mineral appearance unique to Himeji Kurozan.
This slow and demanding work naturally limits production: a single craftsman can produce only a very small number of pieces each month, which explains the rarity of this material on the market.
This leather is available at Jean Rousseau in five colours — black, brown, blue, red, and purple — and can be used for watch straps, small leather goods, and belts. It can also be selected through our bespoke service to create personalised pieces made from this material, tailored to each client’s needs.
Classic 3.5 watch straps in Black Diamond calf, shown here on three Awake watches from the Son Mài Frosted Leaf and Son Mài Silver Leaf “Vignette” collections. The artisanal treatment of their dials, combining traditional lacquer techniques with silver leaf, creates a visual depth that highlights the distinctive texture of this Japanese leather.