Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" agents. Varnish has little or no colour, is transparent, and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from opaque to translucent. http://en.wikipedia.org/wiki/Varnish
On 20 April 1661 SP mentions "indian varnish":
The Indian Varnish for Cabinets, Coaches, and suchlike.
Take the highest rectified spirit of Wine a quart, seed Lake or shell Lake five ounces, put them into a glass body; and dissolve the Lake in Balneo (but beware lest the water in the Balneum boil, for that will turn the Varnish white) this done strain the matter through a Flannel bag, and keep it in a glass bottle close stopt for use.
Where note, 1. That if the spirit is good, it will (if you put Gun-powder into it) burn all away and fire the Gun-powder. 2. That this Varnish done over leaf Silver, turns the Silver of a Gold colour. 3. That this is that varnish which Coach-makers and others use for that purpose. 4. That it preserves the Silver which it is laid upon from the injuries of the Air. 5. That being laid upon any colour it makes it look infinitely the more beautiful. 6. That if it lies rough you may polish it with the impalpable powder of Emery and water.
---Polygraphice: Or the Arts of Drawing, Engraving, Etching, Limning, Painting &c.; W. Salmon, 1685
[Lake, a red colour used in painting, cinnabar.]
[Balneum, a double-boiler]
Many thanks to Bill for this very interesting quotation. However, I would like to correct an important detail, if I may. "Lake" here does not refer to the class of pigments know as "lakes" or "dye lakes." It means "Lac" or, as we would say, shellac. Lac is a natural resin secreted by one of a number of South-Asian insects, most commonly the true lac bug (Kerria lacca), which infests certain trees. The lac harvesters cut the infested branches, scrape off the resin, and grind it into coarse pellets about the size of lentils. In this state it is known as "seed-lac" or "seed-shellak"--"seed Lake" in the text above. A first stage of refinement involves melting and straining the lac granules to remove bits of bark and insect parts. The melted lac is then either cast into pucks (button-lac, button-shellac); or spread out in thin sheets which are then broken up into flakes--"shell Lake" here. Or shellac, as we would say.
Alcohol--"spirits of wine"--is the only solvent for shellac. It must be very high strength to create a good varnish--about 190 proof. The gunpowder method for proofing alcohol is new to me--and very clever it is. The alcohol would have to be very close to pure, or the residual water would wet the powder, which then would not burn. Alcohol of this purity was not available until the early 16th century and not readily available until the 17th. Prior to spirit-varnishes, woodwork was finished with wax or with drying oils, such a linseed oil--still used today.
A final detail: pigments called "lakes" are vegetable dyes combined with some kind of fixative, called a mordant (from the French "mordre"= to bite) that will soften the fibres of the fabric being dyed. Lac was originally used as a dyestuff, so the word "lake" for these pigments derives from the same word that gave us "shellac" The "shell" part also derives from French: "écaille"=a shell, a flake.
The lake-red used by the painters in enamel is composed of fine gold dissolved in aqua regia, with sal armoniac, or common salt. The dissolution being completed, it is put in a cucurbit with spring-water and mercury, over hot sand, for twenty-four hours. The powder remaining at the bottom of the cucurbit when the water is poured off, is ground up with double its weight of flower of sulphur, and put in a crucible over a gentle fire; and when the sulphur, which takes fire, is exhaled, the red powder remaining is ground with rocaille.
Museum Rusticum Et Commerciale. v.1, p.166. 1764.
But then there's this:
LACCA, Lac, or Stick-lac, improperly called gum-lac, in natural history, a concrete brittle substance, of a dark red colour; brought from the East-Indies incrusted on pieces of sticks; internally divided into several cells; said to be the resinous juice of certain trees, collected by winged red insects of the ant kind, impregnated with the tinging matter of the insects, and by them deposited either on the branches of the trees, or on sticks fastened in the earth for that purpose. In the cells are often observed small red bodies, which appear to be the young insects.
The tinging red animal matter of the stick-lac dissolves both in water and in rectified spirit, and appears to be of the same general nature with that of cochineal; like which it is made dull by alkalies, and brighter by acids, and turned to a scarlet by a solution of tin.
Lake was most probably first made from the colour found in the grains of the stick-lac, from whence it seems to have taken its name; but it may be made from a great variety of substances which afford a crimson tinge; though at present it is seldom prepared from any other than cochineal, scarlet rags, and Brasil-wood.
---The Complete Dictionary of Arts and Sciences, Volume 2. T.H. Crocker, 1766.
Chart showing the number of references in each month of the diary’s entries.