Before beginning to varnish, it is necessary that the surface to which it is to be applied, should be perfectly free from all grease and smoke stains, for it will be found if this is not attended to, the varnish will not dry hard. If the varnish is to be applied to old articles, it is necessary to wash them very carefully with soap and water before applying it. When it is wished that the varnish should dry quickly and hard, it is necessary to be careful that the varnish should always be kept as long a time as possible before being used; and also that too high a temperature has not been used in manufacturing the varnish employed. It is likewise customary, when it can be done, to expose the article to the atmosphere of a heated room. This is called stoving it, and is found to greatly improve the appearance of the work, as well as to cause the varnish to dry quickly. After the surface is varnished, to remove all the marks left by the brush, it is usually carefully polished with finely-powdered pumice stone and water. Afterwards, to give the surface the greatest polish it is capable of receiving, it is rubbed over with a clean soft rag, on the surface of which a mixture of very finely powdered tripoli and oil has been applied. The surface is afterwards cleaned with a soft rag and powdered starch, and the last polish is given with the palm of the hand. This method is, however, only employed when those varnishes are used which, when dry, become sufficiently hard to admit of it.
A good surface may be produced on unpainted wood by the following treatment: Glass-paper the wood thoroughly as for French polishing, size it, and lay on a coat of varnish, very thin, with a piece of sponge or wadding covered with a piece of linen rag. When dry, rub down with pumice dust, and apply a second coat of varnish. Three or four coats should produce a surface almost equal to French polish, if the varnish is good and the pumice dust be well applied between each coat. The use of a sponge or wadding instead of a brush aids in preventing the streaky appearance usually caused by a brush in the hands of an unskilled person.
When varnish is laid on a piece of cold furniture or a cold carriage-body, even after it has been spread evenly and with dispatch, it will sometimes "crawl" and roll this way and that way as if it were a liquid possessing vitality and the power of locomotion. It is sometimes utterly impossible to varnish an article at all satisfactorily during cold weather and in a cold apartment. In cold and damp weather a carriage, chair or any other article to be varnished should be kept in a clean and warm apartment where there is no dust flying, until the entire woodwork and iron-work have been warmed through and through, to a temperature equal to that of summer heat - say eighty degrees. That temperature should be maintained day and night. If a fire is kept for only eight or ten hours during the day, the furniture will be cold, even in a warm paint-room. Before any varnish is applied, some parts of the surface which may have been handled frequently, should be rubbed with a woolen cloth dipped in spirits of turpentine, so as to remove any greasy, oleaginous matter which may have accumulated. Table-beds, backs of chairs, and fronts of bureau drawers are sometimes so thoroughly glazed over that varnish will not adhere to the surface, any more than water will lie smoothly on recently painted casings. The varnish should also be warm - not hot - and it should be spread quickly and evenly. As soon as it flows from the brush readily and spreads evenly, and before it commences to set, let the rubbing or brushing cease. One can always do a better job by laying on a coat of medium heaviness, rather than a very light coat or a covering so heavy that the varnish will hang down in ridges. Varnish must be of the proper consistency, in order to flow just right and to set with a smooth surface. If it is either too thick or too thin one cannot do a neat job.
When it is wished to varnish drawings, engravings, or other paper articles, it is usual to give them a coat of size before applying the varnish. For the preparation of Size see article under that head.
If the varnish has been blistered by heat or corroded by strong acids, the only remedy is to scrape or sandpaper the article and revarnish. Spots may often be removed by the following process: Make a mixture of equal parts of linseed oil, alcohol and turpentine, slightly moisten a rag Avith it, and rub the spots until they disappear. Then polish the spot with ordinary blotting paper. Varnish injured by heat can hardly be restored in any other way than by removing it and applying a fresh coat.