The seiwari (背割り) process—literally “back-splitting”—is applied when using bamboo culms in their round form. By creating a controlled slit, the craftsman prevents the bamboo from cracking unpredictably as humidity levels change. Just like round timber, untreated round bamboo is prone to natural splitting over time.

Although the technique itself is simple, it relies on the craftsman’s trained eye to determine exactly where the slit should be made. In this particular case, small-diameter culms are being prepared for an interior project.