This section is from the book "Industrial Recipes", by John Phin. Also available from Amazon: The Workshop Companion.
To fix Pencil Marks so they will not rub out, take well-skimmed milk and dilute with an equal bulk of water. Wash the pencil marks (whether writing or drawing) with this liquid, using a soft, flat camel-hair brush, and avoiding all rubbing. Place upon a flat board to dry.
 
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