Laser-induced shou-sugi-ban process

Wood charring, known in Japan as Yakisugi or Shou-sugi-ban, is a traditional technique to create charred surface by burning. It has been utilized primarily for the preservation of wood used in outdoor applications, such as cladding or fence. The charring process enhances the wood's durability by making it more resistant to moisture, insects, and decay, while also providing a unique aesthetic appeal. In this study, we investigated wood charring by means of laser treatment in a controlled manner.
There are a number of applications for laser treatment of wood. However, conventionally, they are mostly for decorative purposes. Laser cutting or engraving enables to yield complicated designs and patterns. For those applications, laser beam is focused to ensure the resolution and power efficiency.
In this study, a series of char-lines were created on wood (LT surface of Cryptomeria japonica) using diode-laser (Xtool D1 Pro 10W) under various conditions. Focus adjustment was the key parameter, as well as output power and speed. Degree of the char-lines was evaluated by their dimensions (width, depth) and electrical resistance. Crystallization degree was also checked by transmission electron microscopy.
Both width and depth tended to increase with decreasing speed, while defocusing (deviating from the focus point) resulted in increased width and decreased depth. Electric resistance turned out to differ between early wood and late wood, sap-wood and heart-wood. The lowest resistance was in the order of 1 kΩ·cm or less, which is equivalent of white charcoal. This suggests the charring at fairly high temperature (> 800 °C).