[Fig. 61].—Cutting Up Silver Solder into Paillons
Larger Work.
—An example of silver-soldering larger work is the joining together of two pipes, one smaller than the other. The best course to adopt is to file or scrape the end of the smaller and the inside of the larger (reaming and filing them if necessary) until a good fitting joint is obtained, as in [Figs. 59] and [60]. A strip of solder is then cut off, and, after the joint is well coated with borax paste, this solder may be wound round the smaller pipe. If the joint is soldered in a vertical position, the larger pipe should be the lower. The heat should be conserved by laying the work in the coke and building the same round, or, if the work is too large or the joint in an awkward part of the pipe, a shield of tin plate or iron should be placed behind the joint so that the flame is thrown back on to the work. Should the pipe be attached in close proximity to the joint to a heavy piece of metal, then warm this metal up first, otherwise all the heat will travel to this part, and the work will take much longer to get to the proper temperature. In all cases where one part of the joint is of heavier substance than the other, that part should receive the greater amount of attention from the flame.
Quenching Silver-soldered Work.
—Many craftsmen object to the cooling of the work by plunging it into water or pickle whilst it is hot; but no damage or cracking of the joint occurs, it is thought, if the work is not plunged when it is red hot or anywhere near red hot. Plunging into a pickle certainly cracks the burnt-in borax, which can be readily removed and the joint examined to better advantage. Many a silver-soldered joint has been passed as quite sound when it has only been the borax that has been stopping the interstices, and only after it has been placed under service for some time does the faulty joint make itself apparent.
Silver-soldering cannot be done on work that has been previously soft-soldered unless the soft-soldered part is first cut away; but, of course, soft-soldering can be readily accomplished after silver-soldering or brazing so long as the work is clean and all burnt borax is first removed.
Removing Soldering Marks.
—Solder will run away from a part of a joint instead of running into it when the edges of the joint have been imperfectly cleaned preparatory to the application of flux and solder; also, if some dirt has got into the flux, or on the paillons of solder employed. Another cause is unequal heating of the joint, or allowing it to expand too much whilst being heated. The resulting fire marks may be removed by warming the articles on a pan over gas, and plunging them whilst warm into the sulphuric acid pickle. Or the marks may be removed in a hot and strong solution of potassium cyanide, and the polish renewed by a light polishing with a revolving swansdown mop and rouge composition.