The flux ordinarily used for plumber's wiping solder is tallow, generally in the form of a candle. No other fluxes answer this purpose so well, as they all spoil the wiping cloths, but different kinds of fluxes are required for different kinds of work. For a wiped joint, a tallow candle is rubbed over the parts. This is often used in making copper-bit joints, though for this latter purpose many plumbers prefer to use black rosin. Muriatic acid is employed as a flux for use when soldering, the acid - which is a powerful poison - being used for zinc or galvanized iron, and the killed acid for other metals, such as brass, tinplate, copper, wrought-iron, etc.
After tinning brass with fine solder, the copper-bit should be wiped quite clean, as the copper, uniting with some of the zinc in the brass, may affect the wiping solder. Some plumbers tin brass by holding it over the metal pot and pouring the solder on to it. This is bad practice, as the surplus solder, and any zinc with which it may have combined, fall into the pot. In cleaning solder, the sulphur must be used with more care than when cleaning lead, or the tin will be burnt out as well as the zinc.
The method ordinarily adopted by plumbers for tinning iron is to file it bright and then coat the part with killed acid or chloride of zinc, or muriatic acid in which zinc has been dissolved, and then dip it into molten plumber's solder. Sometimes sal-ammoniac is used for the flux, or a mixture of sal-ammoniac and chloride of zinc. When wrought-iron pipes have been thus tinned, and then soldered joints made, they have been found to come apart after a few years, the pipe ends, when pulled from the solder, being found to be rusty. Although more difficult to accomplish, iron pipe ends filed and covered with resin, and then plunged into molten solder, from the surface of which all dross has been skimmed, and afterwards soldered together, have been known to last a considerable time. When tinning the pipes or making the joints, the solder must not be overheated, or failure will result.