« PreviousContinue »
linseed-oil for a few minutes, and strain it. Use
à it warm.
Essential Oil Varnish.
The essential varnishes consist of a solution of resin in oil of turpentine. This varnish being applied, the turpentine evaporates, leaving the resin behind. They are commonly used for pictures.
To dissolve Gum Copal in Oil of Turpentine. Whatever quantity is to be dissolved should be put into a glass vessel capable of containing at least four times as much, and it should be high in proportion to its breadth.
Reduce two ounces of copal to small pieces, and put them into a proper vessel, Mix a pint of oil of turpentine with one-eighth part of spirit of sal ammoniac; shake them well together, put them to the copal; cork the glass, and tie it over with a string or wire, making a small hole through the cork. Set the glass in a sand heat, so regulated as to make the contents boil as quickly as possible, but so gently, that the bubbles may be counted as they rise from the bottom. The same heat must be kept up exactly till the solution is complete.
It requires the most accurate attention to succeed in this operation. After the spirits are mixed, they should be put to the copal, and the necessary degree of heat be given as soon as possible. It should likewise be kept up with the utmost regularity. If the heat abates, or if the spirits boil quicker than is directed, the solution will immediately stop, and it will afterwards be in vain to
proceed with the same materials; but if properly
managed, the spirit of sal ammoniac will be seen gradually to descend from the mixture, and attack the copal, which swells and dissolves, except a very small quantity which remains undissolved.
It is of much consequence that the vessel should not be opened till some time after it has been
perfectly cold. It has happened, on uncorking the vessel, when it was not warm enough to affect the hand, that the whole of the contents were blown with violence against the ceiling. It is likewise important, that the spirit of turpentine should be of the best quality. The turpentine bought at the colour-shops seldom answers; it should be had from Apothecaries' hall.
This varnish is of a rich deep colour, when viewed in the bottle, but seems to give no colour to the pictures it is laid on. If left in the damp, it remains tacky, as it is called, a long time; but if kept in a warm room, or placed in the sun, it dries as well as any other turpentine varnish; and when dry, it appears to be as durable as any other solution of copal.
When resins are dissolved in alkohol, commonly called spirits of wine, the varnish dries very speedily, but is subject to crack. This fault is corrected by adding a small quantity of oil of turpentine, which renders it brighter, and less brittle when dry.
To dissolve Gum Copal in Spirits of Wine. Dissolve half an ounce of camphor in a pint of alkohol, or spirits of wine ; put it into a circulat
ing glass, and add four ounces of copal, in small pieces; set it in a sand-heat so regulated, that the bubbles may be counted as they rise from the bottom; and continue the same heat till the solution is completed.
Camphor acts more powerfully upon copal than any other substance. If copal is finely powdered, and a small quantity of dry camphor rubbed with it in the mortar, the whole becomes in a few minutes a tough coherent mass. above described will dissolve more copal than the menstruum will retain when cold. The most economical method will, therefore, be, to set the vessel which contains the solution by for a few days; and when it is perfectly settled, pour off the clear varnish, and leave the residuum for a future operation.
This is a very bright solution of copal: it is an excellent varnish for pictures, and may, perhaps, be found to be an improvement in fine japan works, as the stoves used in drying those articles may drive off the camphor entirely, and leave the copal pure and colourless upon the work.
N. B. Copal will dissolve in spirit of turpentine, by the addition of camphor, with the same facility, but not in the same quantity, as in alkohol.
A Varnish for Wainscot, Cane Chairs, fc.
Dissolve in a quart of spirits of wine, eight ounces of gum sandarach, two ounces of seed-lac, and four ounces of resin; then add six ounces of Venice turpentine. If the varnish is to produce a red colour, more of the lac and less of sandarach should be used, and a little dragon's blood should be added. This varnish is very strong.
A Varnish for Toilet-Botès, Cases, Fans, &c.
Dissolve two ounces of gum mastich, and eight ounces of gum sandarach, in a quart of alkohol ; then add four ounces of Venice turpentine,
À Varnish for Violins, and other Musical
Put four ounces of gum sandarach, two ounces of lac, two ounces of gum mastich, an ounce of gụm elemi, into a quart of alkohol, and hang them over a slow fire till they are dissolved; then add
; two ounces of turpentine.
Varnish for employing Vermilion for painting
Dissolve in a quart of alkohol six ounces of sandarach, three ounces of gum lac, and four ounces of resin ; afterwards add six ounces of the cheapest kind of turpentine: mix it with a proper quantity of vermilion when it is to be used.
Take spirits of wine, one quart; put it in a wide mouthed bottle, add thereto eight ounces of seed-lac, that is large grained, bright, and clear, free from dirt and sticks ; let it stand two days, or longer, in a warmă place, often shaking it. Strain it through a flannel into another bottle, and it is fit for use.
Take one quart of spirits of wine, eight ounces of the thinnest and most transparent shell-lac, which, if melted in the flame of a candle, will draw out in the longest and finest hair ; mix and shake these together, and let them stand in a warm place for two days, and it is ready for use. This varnish is softer than that which is made from seed-lac, and, therefore, is not so useful ; but may be mixed with it for varnishing wood, &c.
White Varnish for Clock Faces, 8c. Take of spirits of wine, highly rectified, one pint, which divide into four parts; then mix one part with half an ounce of gum mastich, in a phial by itself; one part of spirits, and half an ounce of gum sandarach, in another phial; one part of spirits, and half an ounce of the whitest parts of gum-benjamin. Then mix and temper them to
It would not be amiss to add a little bit of white resin, or clear Venice turpentine, in the mastich bottle; it will assist in giving a gloss. If
your varnish prove too strong and thick, add spirits of wine only ; if too hard, some dissolved mastich; if too soft, some sandarach or benjamin. No other rule can be given, unless the quality of the gums and the spirits could be ascertained. When you have brought it to a proper temper, warm the silvered plate before the fire, (if a clock face, taking care not to melt the wax,) and with a flat camel’s-hair pencil, stroke it all over until no white streaks
appear. This will preserve silvering many years,