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.
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.
327. 3. The Neat’s-Foot-Oil prevents the Varnish from being sticky, or adhèsive: and may be put into the Linseed-Oil, at the same Time with the Lime, or burnt Umber.
327. 4. To make the above Varnish transparent, or white; use Mastic and Copal: to make it brown, use Seed or Shell-Lac, and browner still, use pounded burnt Umber.
327. 5. Rezin, or Chio Turpentine may be added, till the Varnish has obtained the desired Thickness.
327. 6. It must likewise be observed, that Litharge rots the Silk: therefore Trials must be made without the Use of Litharge.
327. 7. The longer the raw Linseed-Oil remains on the unslacked Lime, or Umber, the sooner will the Oil dry, after it is used.
If some Months; so much the better. Such Varnish will set, i. e. will not run, but keep its Place on the Silk, in four Hours.
The Silk may then be turned, and varnished on the other Side.
328. on gum mastic, sandarac, seed-lac, shell-lac, and copal.
328. 1. Gum Mastic dissolves, without pounding, by adding a few Drops of Oil of Vitriol: so do Gum Sandarac, and Gum Copal, when finely pounded and sifted.
328. 2. Gum Sandarac, and Gum Mastic are great Driers of themselves: and may be substituted for Litharge.
328. 3. The Mastic dissolved in the Oil of Vitriol, gives a sweet Smell to the Varnish.
328. 4. Sandarac will soon grow dusk in the Fire: it melts into a transparent Liquor.
328. 5. Sandarac, Seed-Lac, and Shell-Lac, must be finely pounded and sifted, before they are used.
329. The Author having examined different Kinds of varnished Silks, in different Places, does, from their Excellence, recommend those made by Fawkner, Umbrella-Maker, Alport-Street, Manchester; a Person wholly unknown to him, but from the Merit of the Work: which consists not only in the Varnish itself; but in the peculiar Method of applying it, which the Author is not at Liberty to make public.
Fawkner can warrant his Silk Air-tight; soft and unadhesive; durable, and unalterable by that Excess of Heat and Cold, to which the Balloon is, at the same Time, subject; viz. internally, to the hot depredating and caustic Fumes, rising with the Gass: and externally, to the Sun, Wet, Frost, and Drought.
