In first placing the brush on the surface, it should be applied, not close to the edge, which would be liable to give too thick a coat at that part, but at a little distance from the edge, and the strokes of the brush should be directed towards the ends alterlately, with steady rapid strokes and only very moderate pressure. If the surface is small, the whole may be passed over at the one operation, and then the brush may be returned to the edge at which it was first commenced, and it may be passed over the surface in the same manner a second or third time, to distribute the varnish uniformly, and work out the air-bubbles.
Sometimes, in small surfaces, the second series of strokes is made at right angles with the first, in order to distribute the varnish more equally, and the third is laid on in the same direction as the first; but unless this is done expeditiously and equally, it leaves cross lines, which injure the appearance of the work.
Large surfaces are more difficult, as the varnish thickens too rapidly to allow of the entire surface being covered at one operation; they must therefore either be worked gradually from the one edge to the other, as in laying a tint of water-colour, or the varnish must be applied upon separate portions successively; but it is rather difficult to join the portions without leaving irregular marks. It may, however, be successfully executed by thinning off the edges of the first pieces, and allowing the adjoining portion to overlap also by thinning off the edge with light strokes of the brush, made in the same direction as those on the finished portion; but some care is required to avoid disturbing the former coat while it is still soft and easily acted upon by the fresh varnish. In the same manner, in laying on a second or any subsequent coat of varnish, care must be taken not to continue the application of the brush for a sufficient length of time to disturb the previous coat, which is speedily softened by the fresh varnish, and if the application of the brush were continued too long, it would be disturbed, and give the work an irregular or chilled appearance.
Wood and other porous surfaces absorb a considerable portion of the first coat of varnish, which sinks in deeper at the softer parts, and raises the grain of the wood in a slight degree, a second coat is generally necessary to fill up the pores uniformly, and sometimes even a third is required. The work is then rubbed smooth with fine glass-paper, and if the varnish is not to be polished, two or three coats more generally suffice to finish the work, as the thickness of varnish should not be too great, or it is liable to crack or chip.
With the view of economising the varnish, porous surfaces, such as wood and paper, are frequently sized over, to prevent the varnish from sinking into the surface. For dark coloured works thin size, made from ordinary glue of good quality, is generally used; but for light coloured surfaces, a lighter coloured size is used, which is prepared by boiling white leather or parchment-cuttings in water for a few hours, or until it forms a thin jelly-like substance, which is used in the tepid state, and sometimes solutions of isinglass or tragacanth are employed in like manner. For wood the choice, except as to colour, is nearly immaterial, the object being only to prevent the absorption of the varnish by a very thin coat of some substance not soluble in the varnish; but for paper works the parchment size is on the whole preferable, as it is almost colourless, and tolerably flexible. It is better in all cases to use two coats of thin size than one of a thicker consistency, as the size is more uniformly spread in two coats, and there is less risk of any small spots being left untouched, which would show specks in the varnish when completed; but no greater thickness of size should be employed than is absolutely necessary, or otherwise it would be liable to crack and peel off.
The method of polishing the best varnished works has been already describing in the catalogue of grinding and polishing processes, under the head Varnished Works, page 1101, from the practice of Messrs. Erats, from whom many of the above particulars were also derived. The routine pursued in the polishing of japanned works is briefly mentioned at page 1069, and similar methods are used with trifling variations, for polishing all other varnished works.
Ornamental painting on varnished works is executed as mentioned in page 1101, after the general surface has received a ground of about six coats of varnish, and been rubbed smooth and level. The colours employed should be of the best quality, ground as fine as possible with turpentine, and mixed to the proper consistence with the same varnish that is employed for the general surface. So far as convenient the transparent colours are to be preferred, and those principally used are dragon's blood, lakes, Prussian blue, chrome yellow, verdigris, white lead, lamp black, and ivory black. Tincture of saffron is also employed for yellow colours, and also for staining the general surface of a yellow tint before it is varnished; the tincture is made by macerating half an ounce of saffron for two or three days in a pint of spirits of wine; and other coloured stains are sometimes prepared and applied in the same manner.
Turpentine and oil varnishes are applied in the same general manner as the spirit varnishes, but as they dry slower, more time may be occupied in laying on the varnish, and therefore large surfaces may be more easily and uniformly covered; but the same precautions with respect to the dryness and warmth of the atmosphere are likewise desirable, when it is wished to produce a brilliant surface.
In conclusion, it may be observed, that generally speaking all coloured works are first painted of the required tints, and a transparent varnish is afterwards laid on to give the required brilliancy, but for delicate ornamental painting two or three coats of varnish are generally laid on and smoothed down after the general ground has been painted, in order to prepare a suitable surface for artistic works.