The next and most necessary proceeding will be the cleansing of the surfaces that are to be permanently joined. In most instances the application of clean cold water in a sponge will be sufficient, but where much grime and grease have accumulated different means must be resorted to. Soap is not to be recommended but, and especially if the surfaces are irregular, some pure benzine, applied or slightly scrubbed in by a stiff brush, not too large, and the parts then wiped repeatedly on a clean cotton or other absorbent rag. Pure benzine, if not rubbed in too hard or too long, will not injure the adjacent varnish, be it the delicate film on a thousand pound gem of Cremona or the flinty covering of a less presumptuous output from Naples. When evaporation is complete, it will be so in a few minutes, some clean water brushed in and wiped away, will leave the surfaces in a state for receiving glue.
The glue should be of good strength--the junction being intended to be permanent--and applied in a warm atmosphere or the parts warmed a little, as, under different conditions the glue will coagulate or "set" (diagram 18). When the parts are placed properly in position, and the outside blocks or buffers adjusted for opposing pressure, the cramps may be applied and screwed fairly tight. If the surfaces meet well and the pressure is properly distributed, the glue will ooze out at the juncture of the fractured parts. This can be wiped off with a cloth, but occasionally mended parts cannot be got at easily, if so the glue must be rubbed away after cramps and moulds have been removed, by a damp sponge or cloth and then wiped dry. Sometimes differently to the above mentioned simple fracture, it may be of the kind described by surgeons as comminuted or split into small fragments. This will be found to be much more troublesome than the former; after cleansing as usual, if the injured parts are actually separated from the main structure, judgment must be exercised in selecting those portions--the largest if possible--that when glued in, will act as a support for others to be afterwards inserted. The same attention in kind and amount will mostly bring about a satisfactory result, but frequently with this class of fracture minute pieces may have been lost past recovery, leaving a small gap here and there to be filled up somehow. These places, if large enough, should have pieces let in according to the manner before described. If they are too small for this treatment--a little experience will enable the eye to judge at a glance--then the only course will be to fill them up with some kind of paste or improvised mixture. For this purpose a good "stopping" must be made. This has, in olden times as well as the present, been a difficulty to meet. Many kinds of material have been used, most of them having some objectionable quality; some repairers keeping some kind, others generally making further experiments. Among the various materials plaster of Paris or common chalk worked up in glue has been frequently used; it is certainly strong for some time after use, but gradually, as age creeps on, contraction takes place towards the central portion, and a small fissure all round is seen more and more evident, and which gets filled with grime causing a very distinct black line, which draws attention to the spot, the substance also being so much harder than the surrounding wood, gets polished with a little friction and usage and declares its unsympathetic nature; further, it is difficult to colour successfully, or even well, and for these objections it should never be used. Wax is another material that has been extensively in use among the older English repairers, but it has very little to recommend it except handiness, and that quality ought not to be placed in the balance against much more important ones. It is not easily colourable; with usage the top surface gets wiped off, leaving a hollow. Powdered wood with shellac, or the latter with some heterogeneous materials have also failed, as the alcoholic solution destroys the surrounding varnish.