If the stain turns red it contains mechanical pulp. The depth of colour of the red stain indicates the percentage of mechanical fibre present.

• 把它涂上纸面，若痕迹仍然黄色，则不含机械木浆;若痕迹变红，则含水量机械木浆。红色痕迹颜色深浅，表示所含机械纤维的百分率。