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.
By slow heat in an iron pot melt 1/2 lb. powdered copal gum, 2 oz. balsam of capivi, previously heated and added. When melted, remove from the fire and pour in 10 oz. spirits of turpentine, also previously warmed. Copal will more easily melt by powdering the crude gum; let it stand for a time covered loosely.
White hard spirit varnish may be made by dissolving 3 1/2 lb. gum sandarach in 1 gal. spirits of wine; when solution is complete, add 1 pint pale turpentine and shake-well together.