Why is the groove of some swords painted with red lacquer?
You may notice that a BOHI(棒樋) of some swords are often lacquered with red. As red is the color of blood, people tend to assume that a Bohi is designed to allow blood to drain down the groove and sometimes call it “blood groove” but it has nothing to do with blood.
In Japan, red is a symbol of the sun and considered as the color of life. Also, it’s believed to have the power to ward off evil spirits or bad luck. For this reason, some swords have a red Bohi and most of they were displayed at a shine or temple.