ON VARNISHES, CONTINUED.
Section 325. TO those, who are unacquainted with the Principles of Chemistry, or the Books which teach it; and yet are desirous to make Experiments, which may throw fresh Light on this curious and useful Art, when applied to Varnishes for Umbrellas or Balloons; the following detached Notes are recommended: which were communicated to the Author by different Artists; each eminent in his Profession.
326. To make copal Varnish.
Procure some bluish Flemish alcaline Ashes, (an Ounce suppose): pound them very fine, and lay them before the Fire, till they become hot and dry.
Put them, while hot and dry, into Oil of Turpentine, (a Pint or Pound for Instance): or, into the same Quantity of Spirits of Wine.
For by Means of the Alcaly,[109] all the Water invisibly contained in the Oil or Spirits will be absorbed, and leave the Oil or Spirits, alcohol, that is, quite pure, and highly rectified: which Process is called alcalizing the Turpentine, or Spirits.
Put the Turpentine or Spirits so alcalized, into a Copper Vessel, with half an Ounce of yellow copal finely pounded and sifted.
Stir it, and the Copal will soon melt.
N. B. If you alcalize the Spirit of Turpentine, when the Copal is dissolving, add a little Spirit of Wine: and if you alcalize the Spirit of Wine, when the Copal is dissolving, add a little Spirit of Turpentine.
The sediment of the Varnish will dry on the Silk, in a few Hours.