Dirty cycle or other machinery oil may be filtered through cotton-wool, flannel, or any similar material without affecting its lubricating properties. Flannel is not so good as closely packed cottonwool, because the fibres are openly felted and the finer dirt can get through. Closely packed cotton-wool makes a slow filter. The best filtering arrangement is a glass or tin funnel placed in a bottle, and a circle of best white blotting paper folded twice and opened to fit the funnel. The oil will pass pretty quickly through the paper. When the blotting paper begins to plug up it may be removed and fresh paper substituted.