The Silk shoud be stretched all Ways horizontally, by Pins or Tenter-Hooks, on Frames; which Frames, the greater they are in Length, the better: and the Varnish poured on +cold+, in _hot_ Weather; and +hot+, in _cold_ Weather. It is _perhaps_ best, always to lay it on, when _cold_. The Art of laying it on properly, consists in making +no intestine+ Motion in the Varnish, which woud create minute Bubbles. Therefore Brushes of every Kind are improper. Each Bubble breaks in drying, and forms a small Hole, throu’ which the _Air_ will _transpire_. CHAPTER LXIII. 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. The thicker the Varnish, the sooner it dries. [Sidenote: To make _thin_ Varnish.] 327. Article 1. To make an excellent +thin+ Varnish. To one Quart of _cold raw_ Linseed-Oil poured off from the Lees made by a Lump of _unslacked_ Lime on which the Oil has stood, ten or eight Days, at the least, in order to communicate a drying Quality: (or on _brown Umber_ burnt and pounded, which will have the like Effect:)—add half an Ounce of Litharge. Boil them for half an Hour. Then add half an Ounce of _the Copal Varnish_. 327. 2. While the Ingredients are on the Fire, in a Copper Vessel; put in one Ounce of Chio Turpentine, or common Rezin: and a few Drops of +neat’s-foot-oil+: and stir the whole with a Knife, or any clean Thing. When _cold_, it is ready for Use.