Restoration of Pictures. The restoration and the cleaning of pictures may be considered together: though cleaning, of course, more strictly applies to the removal from their surface of the accretions of dust or discoloured varnish which obscure their beauties, while restoration refers to the reparation of actual flaws in their surfaces of paint, or in the canvas or wood upon which the paint is laid. When a mastic varnish has been used by the painter, and has become discoloured and opaque, it may be removed by careful and gentle friction with the points of the fingers, previously covered with a resinous powder, which frays off particles of the hardened coating in the form of a fine white dust. When copal varnish has been applied, its removal is more difficult and dangerous, and is usually effected by an application of weak alcohol, spirits of turpentine, and oil. A pad of cotton wool is saturated in this mixture, and passed over the surface of the varnish, which it dissolves and removes; a similar pad steeped in pure oil being applied at intervals to stop the action of the spirit when it threatens to disturb the colour beneath the varnish. When portions of the paint or of the ground of priming on which it has been laid have been removed, these are sometimes filled up to the level of the remaining portions with glue, size, and chalk, and then carefully repainted with dry colour to match the surrounding portions of the surface.
The injuries of time to the various materials upon which colours are laid are very various, and require careful and skilful treatment. In panel pictures worm-holes must be carefully filled up with the last-named composition, and matched with the adjacent portion as just described. If the wood has split, its edges must be carefully brought together, and fastened securely with 'buttons' of hard wood; or the entire back may be protected with a kind of grating of mahogany spars, so adjusted as to admit of a slight contraction and expansion of the panel in varying temperatures. If the panel be too far gone to admit of this treatment, the wood is carefully removed by tenon-saws, planes, and files, till only the surface of priming and colour remains, which can then be remounted on canvas or a fresh panel. If the picture is on canvas which has become decayed, it may be 'relined' by having its back securely fastened, by paste or glue, to a new canvas, and afterwards ironed, a process which has the effect of restoring evenness to a cracked surface of paint; though if the artist has worked with a thick impasto the raised points of colour are apt to become flattened, and the character of the handling to be slightly altered. When a fresco has to be removed from a wall this is usually effected by pasting its surface on paper, and then with a chisel slowly detaching the mortar which bears the colour from the stones upon which it has been laid, each portion, as it is gradually withdrawn, being coiled on a large cylinder. All the operations to which we have referred require extreme caution and great practice for their successful accomplishment. When they are entrusted to careless and untrained hands damage is certain, and it is impossible to estimate the immense amount of injury to works of art that has been effected by ignorant picture-restorers. Proper care of a picture, however, and preservation from damp and dust, will obviate the necessity for its being subjected to restoration; and such protection may be most simply effected by carefully closing in its back, and by covering its surface with glass, which answers all, and more than all, the preservative purpose of varnish, with the additional advantage that it does not chill and discolour with time. Glass is being largely adopted in the great public galleries, for covering even oil-pictures, and it has only one disadvantage—its tendency to reflect the objects placed opposite it, and so to interfere with the ready and complete examination, as a connected whole, of the entire surface of a large, and especially of a dark, painting.