This naturally is the most frequent requirement. Indeed by far the larger number of paintings which are now rather disfigurements than ornaments to the rooms in which they hang, require nothing else to restore them to their original brilliancy of coloring and delicacy of detail.
Many paintings which have grown dark and dim till they are scarcely more than brown and black spots within their frames, many portraits, once brilliant but from which now only the face peers forth dimly and ghostly, owe their present lamentable condition solely to the accumulation on the surface of successive layers of dirt which have been absorbed by the varnish. Fortunately, however long this dirt has been gathering, it may be removed by proper treatment.
This implies both skill and long experience. The same treatment can by no means be applied to all paintings. It must be regulated by the style of the painter : whether he employed his colors solid or very moist, with oil, etc. Much depends also upon the groundwork of the painting, whether it was copper, paper, wood or canvas, and what sort of canvas, as well as the kind of preparation it underwent before receiving the picture.
All this of course can only be apparent to one well acquainted with the mechanical methods of all the schools of art. A beginner, unable to discriminate, runs serious risk of doing harm. In the smooth style, where scarcely a brush mark can be seen, there is grave danger of roughening the surface or of wiping out completely the fine hair lines, scarcely perceptible to the eye, yet giving each its touch to the finished work. In the case of paintings which, like the brilliant works of Turner, are done in what is called the “fat” style, that is, with points or ridges of color left standing upon the surface it is highly necessary to use caution les the sharpness of these ridges be dulled and the painting lose much of its force and character.
The experience of two generations has toughed us the care and discrimination needed for the handling of all oil paintings. We are thus able to do the work of cleaning not only easily but safely, quickly—and therefore cheaply.