Cyclopedia of Painting/Varnishing
VARNISHING.
Two grades of varnishes will usually be required by the painter, inside and outside. That which is used outside will cost a little more than that intended for the interior, as it must be made of materials to resist the weather. If the color of the work is dark, oak varnish is the best to use, but there are various grades of pale varnishes suitable for very light work, some can be obtained which have very little color at all. A special grade of varnish is made for application to wall paper, this, however, is a common grade of varnish, and is not recommended. It is much better to pay a little more and get a good copal varnish. Before paper is varnished it is necessary to give it two coats of size. Concentrated size powder may be used for the purpose, two coats are necessary, so as to ensure no portion of the work being missed. If this is not done the varnish will soak in the paper and leave a nasty black mark.
As a rule, a paper wall should not be varnished. The distempered surface of an ordinary paper looks much better, and it may be kept quite clean if it is frequently brushed down lightly. Dadoes are used in halls and staircases because they assist in giving a finished effect to what would otherwise have a mere bare appearance, and also because when varnished they prevent soiling of the paper by dirty hands. The dado is twice sized, care being taken to apply the size a little above the edge of the dado, so as to prevent the varnish running.
The application of the varnish to either paper or wood work requires some care. The painter is apt to try to get over the work too quickly by taking too much in his brush at once, and this is certain to lead to nasty running or tears. The best way is to dip a little more than the tip of the brush into the varnish, to apply it almost in the same manner as paint across the work, and then to finish by lightly stroking the surface all in the same direction with the tip of the brush, so that the varnish flows and the brush marks are obliterated. Special brushes are required for varnishing, and it is useless to attempt to do good work of this character with an ordinary paint brush. There is no economy in buying a cheap varnish brush. The work done with one is very likely to be marred by the bristles coming out, and such tools only last a comparatively short time. A varnish brush when put aside for a day should be put in either raw linseed oil, or, better still, in some of the same varnish in which it has been used. It should be suspended and on no account to be left to rest upon its bristles. When not required for further use for some time it should be washed out first with raw linseed oil, and then with turpentine, and then wrapped in paper and put away in a cool dry place.
When to Varnish. It might appear that it is unimportant when varnish is applied so long as the work is inside, and is not exposed to showers of rain. As a matter of fact, varnish is the most susceptible material used in painting, and the better quality it is the more sensitive is its nature. In hundreds of cases of varnish which turned out badly, it is safe to say that in nine cases out of ten the trouble is to be attributed simply to the state of the weather. If varnish is applied on a foggy day, for instance, it is almost certain to bloom, that is, a dull appearance almost like the bloom on fruit will appear on the surface. This is difficult to get rid of, although a rag dipped in kerosene oil passed over the surface will often assist. It sometimes happens that a day may be free from rain, and yet a very bad one to do varnishing because the atmosphere may be charged with humidity. A dry day and a warm one is the best for applying varnish. Still, there are other considerations which should not be overlooked. A hall which was varnished showed on one side very badly, while the other side was apparently perfect, the same varnish being used by the same workman. Such a case appears to be somewhat mysterious, the explanation of such cases is probably that the weather was cold, that the door was open during the process of varnishing, which chilled that portion of the surface reached by the cold air.
Varnish manufacturers who understand quite well the nature of their products take care to mature their varnishes by storing them in tanks for months together, and in all well-regulated varnish factories the temperature of the maturing room is kept uniform the year round, for unless this is done the products would vary greatly in use, and give a great deal of dissatisfaction. It will be seen from this that in putting varnish aside it is necessary to store it in a warm place, and to take care that it does not get chilled, if it should become very cold it is well to gently heat it before using it. In piano factories, carriage shops, and in any other places where the varnished surface must be very brilliant and uniform, it is often the custom to take the most painstaking care to prevent any marring of the varnish by cold, draughts, or dust. The temperature is kept always uniform by means of steam or hot air pipes, double doors and windows are used, and sometimes the precautions taken go to the extent that all the air entering the room is thoroughly strained and freed from dust. The workmen have clothes which they put on previous to entering the room. It is not suggested that painters should take any precautions of this kind, but mention is made of the subject here in order to impress them with the necessity of taking the greatest care with varnishing.
There are two additional reasons which give rise to unsatisfactory varnishing. The first is the habit of mixing varnishes. Experienced painters will sometimes assert that they can get a better result by mixing two varnishes together than they could by using only one. There is some excuse for the practice when the supply of a certain varnish runs out, but ordinarily it is entirely against common sense. Varnishes are made for so great a variety of purposes that there is no necessity to mix two together. A moment's reasoning will make it clear that if two varnishes mixed together would give a better result than either one used separately, that the varnish manufacturers themselves would make such a mixture before sending the varnish out. It is quite possible that the ingredients from which the varnish are made would react detrimentally one on the other. It is therefore strongly advisable for the painter not to mix varnishes under any circumstances.
The second objectionable practice alluded to is that of thinning the varnish by adding linseed oil to it; in cold weather varnish sometimes pulls, that is, it is so thick that it is a little difficult to apply without considerable strain on the wrist. In such eases the workman will sometimes add the oil, which may not show up at the time, but it is sure to eventually prove disastrous. Cases have been known where the painter, to save himself trouble, has smuggled in a small bottle of linseed oil, and has added it surreptitiously to the varnish, and caused a great deal of complaint to the manufacturers. In the above remarks only turpentine and oil varnishes have been referred to, not spirit varnish. This, however, is almost invariably mixed with stain as far as the painter's use is concerned. Under the head of Staining will be found information on this subject.
Varnishing can only be properly done by means of brushes specially made for the purpose. There is a very useful grade of varnish made which is known as rubbing varnish. This is applied in the ordinary way, and is, when dry, rubbed down with felt and water dipped in powdered pumice stone. Several coats are usually given, each being rubbed down.