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I have a set of rubbers which I used during my pencil drawing sketches, as shown above.Shading techniques I adopted, make use of rubber very much. Consider myself as a self trainer and so do not blame me on this technique. On taking my rubbers back after some months for a new drawing, I am forced to remove the charcoal droppings on it. Can you propose me the best and easiest method to do it, with less time loss?