They are also called "Bengara-koshi" because many of them are painted with a paint produced by mixing a material containing, as a principal component, particles of ferric oxide (red rust) called "Bengara," and egoma seed oil.
多くは、紅殻（べんがら）と呼ばれる酸化第二鉄（赤サビ）を主成分とした粉末にエゴマ油などを混ぜて塗られているため、紅殻格子とも呼ばれる。