This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
This is a preparation sometimes employed by painters when they are obliged to leave work unfinished for a length of time. Cover the already painted parts with it; it will preserve the freshness of the colours, and can be easily removed on returning to the work. It is made as follows: - Take 1/2 oz. best mastic, finely powdered, and dissolve it over a gentle fire, in 3 oz. very clear nut-oil. Pour the mixture into a marble mortar, with 2 dr. pounded sugar of lead at the bottom. Stir with a wooden pestle, and keep adding water in small quantities till the whole has the appearance and thickness of cream, and refuses to admit more water, so as to mix freely.