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Quote from “A Manual for Amateur Telescope Makers”, Karine, Jean-Marc, Lecleire, Willmann-Bell publisher.
Page 101, para 3 half way through. ’To harden pitch, warm it over medium heat for an hour or two, without quite letting it boil. Just a hint of smoke should escape from the pitch, which is evidence that it is losing some of its solvents. Occasionally take a sample with a spoon, cool it under running water for 10 minutes, and test its hardness with your thumbnail or the stainless steel ball’.
Para 4. ‘To soften pitch that is too hard, add a little turpentine to the melted pitch in the saucepan. ...’
It’s an excellent book worth getting if it becomes available again through Shopatsky. (Not yet listed).
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