An eminent artist and friend of the author passed oxgall over a very dirty old picture, which resisted washing with soap, repeating the application of the oxgall during several days, but without washing it off, till the last day, when a sponge and water easily removed the oxgall and dirt together, leaving the picture beautifully fresh and clean; the efficacy of this very safe method is due to the animal alkali contained in the gall.

Another friend, known to the public as an eminent engraver, was equally felicitous in restoring the purity of an excellent picture, by carefully washing it gradually, and in parts with some of the aqua fortis used in engraving, and cautiously sponging with water as he proceeded.

He found the acid equally efficacious in cleaning the gilding of frames. The principle of safety in this case is, that acids, when not excessively powerful, do not act on the resinous varnishes and oils used in painting; and that nitrous acid does not act upon gold; but there is danger if the picture is cracked or abraded, both for the colouring and the canvas, and it can be employed with safety on oil-gilding only.

This method is the opposite of the alkaline process, and they may be employed together alternately in some cases to remove spots, in doing which all manner of agency must occasionally be resorted to.

Among other ingenious means of cleaning, we have it on the authority of a talented and experienced friend, that by damping the face of a picture, and exposing it to the action of a frosty night, all foulness will be effectually loosened and removed by the subsequent use of a sponge.

In every method of cleaning there is great danger of removing the glazings and otherwise injuring the colouring of a picture, which require great skill and judgment to restore.

In filling cracks and replacing portions of the ground, putty formed of whitening, varnish, and drying-oil, tinted somewhat lighter than the local colours require, should be employed; as plaster of Paris may also in some cases; and, in restoring colours accidentally removed, it should be done with a vehicle of simple varnish, because of the change of tint which takes place after drying in oil: so much is necessary, but in no case is gratuitous painting on an original picture of merit to be justified.

There is a state of declining health which occurs to every picture in the course of time, arising from the natural oil that clothes its colours and forms a semi-opaque skin, or thin surface, which, after being removed, and the picture lined if requisite, and varnished, conduces greatly

to its perfect state and preservation. This operation, which gives freshness without the crudeness that belongs to pictures which have not been ameliorated by time, is necessary to every work deserving reputation.

We have thus recounted various occasions, and described a variety of methods, for the cleaning and preserving of pictures; nevertheless, we earnestly recommend that no inexperienced person should attempt to clean a valuable picture by any more powerful means than is afforded by soft water and a sponge.