By a carefully-calculated mixture of soft and hard gums, with a little transparent colouring matter when necessary, a very good if not highly successful imitation of the surrounding work can be accomplished, such as will prevent the repair "catching the eye" too soon, for it must do so eventually when hunted for. The density of colouring and thickness of the principal component parts must always be studied, as the same depth of tint by a very thin layer as that of a thick one will not have the same effect, and one or the other, when making a contrast with the adjacent old surface, will be conspicuous as a failure.
A few hints may be acceptable as to material and the management of it. We will assume, for instance, that a portion of the upper table of a rather deep brown-red old master has been repaired, and a slice of comparatively light coloured or new wood has been inserted as a necessity, the grain as a matter of course having been matched to the best of the ability of the repairer.
The first step taken will be that of putting a nice clean even surface over the fresh wood, and in such a manner, that on passing the hand or finger over it, no lumps, edges, or rough spots are felt. Having brushed the dust or powdered wood away, the colour of the wood will have to be lowered or subdued, otherwise the whiteness will obtrude itself and stare through any carefully selected varnish. This, for good effect, will be found advisable with the repairing of any old instrument.
The precautions to be taken at this stage are respecting the quality or disposition of the stain (as we may call it). The stains ordinarily sold for colouring wood are quite useless for present purposes, as they are absorbed between the threads, leaving these by contrast very light and the reverse of what is desirable.
A very weak solution in water of bichromate of potash will lower the colour sufficiently for most purposes, and when quite dry the wood will (having swelled with the moisture) require the fine glass-papering again, after which, the next stage can be proceeded with.
The solution of nitric acid in water should be avoided, as, although giving a fairly good lowering of the tint, it destroys the soft parts of the wood, and, further, causes an odour that may cause annoyance to the musician and suspicion to the expert.