An excellent way to preserve an oil-picture from the injuries of damp, mould, and mildew, is to take the precaution of covering the back of the canvas (before nailing it on the straining frame) with a coating of common white lead paint; and when that is dry, give it a second coat. If you buy a picture that has been framed without this precaution, do not neglect having the back of it coated as above, before you hang it up.
The simplest way of cleaning an oil-picture, is to mix some whisky and water very weak. If the mixture is too strong of the liquid, it may take off the paint, or otherwise injure it. Dip into the mixture a very soft and very clean sponge, which you must first ascertain to be perfectly free from sand, grit, or any extraneous object. A good way to soften and clean a sponge, is to boil it in several successive waters, till there is no longer any appearance of sand at the bottom of the vessel. Having carefully washed the picture with the sponge and whisky-water, dry it by going over it with a clean soft silk handkerchief. This is all that can be safely attempted by any one who is not a regular picture cleaner. Therefore, if the picture is smoked or much soiled, it is best to send it to a person who makes picture-cleaning his profession. Many a good picture has been destroyed by injudicious cleaning.
Till it has been made perfectly clearly no picture should be re-varnished; otherwise the fresh varnish will work up the dirt, and make it look worse than ever. As long as a picture is the least wet (either with paint or varnish) it should be carefully guarded from dust; the smallest particles of which by drying into the surface will injure it irreparably. No sweeping or dusting should be permitted where there is a picture not perfectly and thoroughly dry. If there is a fire in the room it should not be stirred, replenished, or touched in any way till the picture has been previously carried out, lest some of the flying ashes might stick to it.
When a picture is finished, it would always be well for the artist to inscribe on the back of the canvas the subject of the painting, the date of its completion, his own name and that of the person for whom it was painted. In short, a concise history of the picture, arranged somewhat like the title-page of a book. Had this excellent practice always prevailed, there would be no occasion for any doubts and controversies concerning the works of the old masters.
The large wooden box for the easel and other things indispensable to a portrait painter, when travelling professionally, should be made broad, low, and square, so that it may be used as a platform on which to place the chair of the sitter. When unpacked of its contents, and appropriated to this purpose, the box must be turned bottom upwards, and concealed under a cover of carpeting or drugget brought along with it. The cover should fit smoothly and closely, and be so made that it can be lifted off, and folded up, whenever the platform is again to be used as a box.