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.
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_.