Pictures form a valuable, though not a necessary, part of domestic furniture; and, as they are liable to become obscured by dust and smoke, or otherwise damaged, various expedients have been contrived to clean them. With this view, an ounce of tartar, and a similar quantity of glass-wort, may be boiled in a pint of water, till the liquor be reduced to one half,when it should be strained : while lukewarm, a sponge is to be dipped in the fluid, and rubbed over the picture ; which must be washed immediately after with tepid water, and gently wiped till it become dry. A few whites of eggs are now to be beaten up, and applid with a feather to the painting, which will thus acquire a fine varnish.
As, however, the ingredients used by the painter often vary in different pictures, there can be no general rule given for removing superficial impurities ; because the success of the experiment entirely depends on the application of proper substances ; such as are capable of combining with dust, smoke, etc. without affecting either the varnish or colouring matter. — Hence, the safest process will be that in which the mildest means are employed : of this nature is the following expedient:—Let the picture be first taken out of the frame, then covered with a clean napkin, which should be moistened with pure water, and suffered to remain in that state for a fortnight or longer, according to circumstances. During this period, the cloth should be occasionally wetted, till it has loosened or softened all the adventitious particles on the surface. A small quantity of purified linseed-oil is now to be passed over the picture, which will thus, in most instances, resume its former lustre. For cleaning very old paintings, it has been recommended to make a ley of rain-water and wood-ashes, or preferably with purified pearl-ashes ; and to cleanse them carefully with this lixivium. Such applications, however, as well as those of soap-water, spirits of wine, turpentine, etc. require to be employed with great precaution; bc-B cause they are apt to corrode the oil of the painting, and thus expose the colours to material injury from the slightest friction. Alkaline solutions, or spirituous liquors, therefore, should be used only for particular spots, that have resisted the action of simple water, the oil of olives, or fresh butter. If these substances were timely resorted to, they would, in general, restore the picture to its pristine beauty, without affecting the delicacy of its shades.