Pictures in oil.,Are exposed to nearly as much dirt as our windows, but for fear of damage we endure much more dirt on them than on the windows before we determine to clean them, the consequence is, that for two-thirds of their duration we behold them through a sickly brown-yellow film of dirt, which quite alters the silvery-grey and pale-purple tints, and which reduces the picture much below its original beauty. Added to this, the varnish most in use for pictures is the mastic, the weakest of all, and one that imbibes the brown dirt of a London atmosphere quite through its substance, so that dirt cannot be washed off. The turpentine, or spirit copal varnish, will not imbibe the dirt, therefore, it may be washed clean. In other respects the goodness of varnish depends on its absolute freedom from moisture, which retards drying and causes the bloom called chilling. Oil is also bad in enabling the varnish to imbibe the dirt instead of leaving it on the surface. I, therefore, never use any varnish that is made with oil for any outside surface. The two best varnishes known is the pure copal and the colourless lac varnish; either of these when dry completely shuts up the picture from any influence of the atmosphere; nothing passes through them, the dirt can only lodge on their surface, and that may be removed by plain washing with flour and water, and if the dirt is more obstinate a thin coat of paste in the act of drying will stick to the dirt, and as soon as dry it may be softened with water and washed off, taking the dirt with it. Copal varnish, after washing, may have its gloss restored by a little varnish thinned with alcohol. There are many difficulties attending the use of oil, for no varnish will effectually protect but such as dry hard and brittle; if such varnish is put on new picture before the oil has hardened, it is very liable to cause cracking over the surface, but old pictures that have become hard, when they are effectually cleaned, may be preserved from all future wear and tear by a good covering of copal varnish, which can be cleaned without removal. New pictures, whilst the artist is living, are liable to retouching; if that is done over the varnish they will be liable to suffer in any future cleaner's hands. On this account,and for the sake of the pictures, it is often desirable to entirely remove the varnish; and this may be done without harm if we first use a water varnish that will not crack the picture, and then cover it with the varnish we esteem best. Isinglass or parchment glue are [58-59] good mediums, but used alone would be very liable to crack the paint; I therefore soften either of these with carbonate of ammonia, white sugar, and the whitest soap; these all tend to reconcile the watery coat to the oil or varnished surface, making it take better hold and spread easier. The soap softens this medium enough to hinder its cracking the picture, and the sugar improves the solubility and transparency. Having well coated the picture with this, let it be soon dried for the sake of keeping it clean, and then cover it with the proper varnish. Whatever the varnish may be its double and dissimilar coating will insulate the picture effectually from the atmosphere, and at any future period both may be removed by rubbing with warm water and flour, which soon finds its way to the water varnish, and softens it enough to be washed off, leaving the picture quite as clean as when first put on. Above I have only stated the means of keeping the picture clean and insulated from the atmosphere by one good varnish, or two dissimilar ones, by which their removal is much facilitated; but this is not enough, if the picture is not protected from being broken all over into thousands of small cracks. This cracking is often laid to the charge of [59-60] the artist, or the materials he paints with, when the fault is not in the material but in the unprotected state of the canvas. It is left to swag about, when moved; or when cleaning, or dusting, it is bent in every part of enough to cover it with minute cracks, at that time invisible, but which gradually become visible, and then the paint is blamed because it will not remain for ever flexible enough to bear such unnecessary usage: a back-board ought, therefore, to be fitted in close to the back of the canvas to support it against all rough usage of that sort. If a painting is hung high, it is eligible to slope it forwards to meet the eye, the canvas will then swag forwards and be shaken by motion of the air on opening doors or windows, the varnish always becoming brittle (otherwise it would not resist dirt) will crack by this motion of the canvas. I saw a picture, six feet wide, that had a good varnished face so placed and it began simmering all over like a tea-kettle previous to boiling. If the canvas had been stretched enough to prevent this swagging, that alone would have cracked the picture as much, and worse, in that it would open the cracks and sooner make room for dirt that can never be removed; all this may be prevented by covering the back-board with pitch and bees-wax, the very act of wiping [60] or dusting the picture will press the canvas enough to cause its adhesion, and thereby prevent any future shaking, and above all, save it from being again stretched. Next, the canvas is usually left to decay. It appears a great oversight to place so much talent and property on canvas and then leave that to decay, for the size which is used to prepare the canvas for priming greatly contributes to the rotting of the canvas, it being exposed to every alteration of the atmosphere. This should be prevented by perfectly drying the canvas with the primed side towards the fire, and then varnishing the back to shut out all future moisture. A picture so preserved and having an adhesive back-board would endure for an unknown period.,P.S. -On the back of every picture there should be a statement of the last process to which its face was subjected in order to guide the next person who has to clean it. ,Cornelius Varley.,