The diseases and disorders which injure and destroy pictures are almost as numerous as those of animal nature, and dependent on similar causes and accidents: hence picture-cleaning has become a mystery, in which all the quackery of art has been long and profitably employed, and in which every practitioner has his favourite nostrum, for doctoring, which too often denotes destroying, under the pretence of restoring and preserving. The restoration of disfigured and decayed works of art is, nevertheless, next in importance to their production; and, as it chiefly relates to the colouring of pictures, it is a part of our inquiry with which we will close the technical portion of our work.

Of the importance of this minor function of the art of painting, a just estimate may be formed by considering that there is no limit to the time an oil-painting may be preserved with all the merit of its original production, by ordinary care and attention, - that a picture so preserved is of even increasing value and interest; and that, but for the spirit of negligence and destruction, modern art might have been elevated, the heart might stilt have been warmed, and possessors ennobled, by the famed works of a Zeuxis, a Protogenes, or an Apelles, the loss of which we have so much reason to deplore.

The medication of pictures is then no mean subject of art, but is, when divested of quackery and fraud, as honourable in its bearing as any other form of healing art; and, to be well qualified for its practice, requires a thorough education and knowledge in every thing that relates to the practice of painting, or the production of a picture, but more particularly to its chemical constitution and colouring. As, however, a picture has no natural and little of a regular constitution, it will be difficult to give general rules, and utterly impossible to prescribe universal remedies for cleaning and restoring pictures injured by time and ill-usage; we will, therefore, briefly record such methods and means as have been successfully employed in cleaning and restoring in particular cases, with such cautions as seem necessary to prevent their misapplication, confining our remarks to oil-paintings in particular.

These are subject to deterioration and disfigurement simply by dirt, - by the failure of their grounds, - by the obscuration and discolourment of vehicles and varnishes, - by the fading and changing of colours, - by the cracking of the body and surface, - by damp, mildew, and foul air, - by mechanical violence, - by injudicious cleaning and painting on, - among a variety of other natural and accidental causes of decay.

The first thing necessary to be done in cleaning and restoring is to bring the picture to its original plane and even surface, by stretching, or, if sufficiently injured to require it, by lining, which, with the transferring of pictures to new canvasses, is an operation admirably well performed in London by experienced hands. In cases of simple dirt, washing with a sponge or soft leather and water is sufficient, with subsequent rubbing of a silk handkerchief; which latter, occasionally used, is eminently preservative of a painting.

After restoring the surface to its level, and washing, the next essential in cleaning is to remove the varnish or covering by which the picture is obscured; and this in the case of simple varnishes is usually done by friction or solution, or by chemical and mechanical means united when the varnish is combined, as commonly happens, with oils and a variety of foulness.

In removing varnish by friction, if it he a soft varnish, such as that of mastic, the simple rubbing of the finger-ends, with or without water, may be found sufficient; a portion of the resin attaches itself to the fingers, and by continued rubbing removes the varnish. If it be a hard varnish, such as that of copal, which is to be removed, friction with sea or river sand, the particles of which have a rotundity that prevents their scratching, will accomplish the purpose. Friction by a rubber of caoutchouc, or India-rubber, is sometimes preferable to the fingers in removing varnish; being clastic and of a resinous nature, it has an affinity by which it attaches itself to the varnish while rubbing, and removes it safely and expeditiously; and rubbers formed thereof will be found very useful tools in the operation of cleaning.

More violent means are sometimes resorted to, hut never without danger or injury.

The solvents commonly employed for this purpose are the several alkalies, alcohol, and essential oils, used simply or combined. Of the alkalies, the volatile in its mildest state, or carbonate of ammonia, is the only quo which can be safely used in removing dirt, oil, and varnish, from a picture, which it does powerfully; it must, therefore, be much diluted with water, according to the power required, and employed with judgment and caution, stopping its action on the painting at the proper time by the use of pure water and a sponge. These cautions are doubly necessary with the fixed alkalies, potash, and soda, which ought to he em-ployed only as extraordinary means of removing spots that will not yield to safer agents. Spirits of wine or alcohol, and ether, act in a similar manner, and their power may be in like manner tempered or destroyed by dilution with water. The uniform disadvantage of alkaline agents is that they obscure the work, so that the operator cannot see the good he is doing, or the mischief he may have done, in the progress of his work, except by revarnishing or oiling out.

This inconvenience is, however, avoided by the safer and better mode of cleaning and removing the varnish at once by spirit of wine, tempered more or less with oil of turpentine: the practice in this case is to apply the spirituous mixture to the surface of the picture with a brush, or with carded cotton; and when, by the motion of either, the liquid has performed its office, its farther or injurious action on the design is to be stopped by another brush or cotton imbued with linseed oil, and held in the other hand; thus alternately proceeding with these tools, till the cleaning and removing the varnish is accomplished. The brushes act rather the better of the two, but the cottons imbibe the dirt and foul liquid, and are then easily exchanged for new ones. The great advantage of this method is, that the design and colouring bear out, and the progress of the cleaning is apparent.