This section is from the book "Soldering For Workshop, Farm And Home", by John Bonert. Also available from Amazon: Soldering For Workshop, Farm And Home - Information On Soft And Hard Soldering - Projects For The Workshop Explained And Illustrated.
Some mechanics refer to the soldering copper as soldering iron or soldering bit. When the term soldering iron is used it would seem that it was made of iron. Copper is used as this metal is a very good conductor of heat. It is also very easy to tin. There are various types of coppers as regards shape, weight and heating. The electric copper is used in the home or work shop where electricity is available. It can be bought with long, short or cupped tips. Where a heavy copper is needed it is better to use the type which is heated over a gas or gasoline flame. These coppers can be had either pointed or hatchet shape. A good many tinsmiths still use the hatchet copper which is quite heavy and naturally holds more heat than the pointed copper. The shank is made so the copper can be turned and used at different angles. Soldering coppers are classed by weight in pairs. For instance, a two-pound copper weighs only one pound as they are listed two pounds per pair. Figure (2) shows some coppers most frequently used.
The small solder pot attachment shown in Figure 2 is used where small articles or twisted ends of wire are to be tinned by dipping them into the molten solder. It is interchangeable with other tips on electric coppers. Electric Coppers are rated according to the current consumed and range from seventy-five to as high as six hundred watts. The copper tips come in different shapes and sizes, some straight and some angle.
There are several methods for tinning the soldering copper a few of which will be given. In the case of a new copper the point can be cleaned with a piece of emery cloth or sand paper to get down to new metal. A copper that has been tinned before will have to be cleaned with a file. It will be noticed that sometimes the surface which was tinned before has become hard or flinty. The file will just slide over the surface without cutting. To remove this hard scale let the copper heat until it is red hot and dip it quickly into cold water. This will help to remove some of the scale and soften the surface and make the filing easier. One thing to keep in mind is that once the copper has been tinned it must not be allowed to become red hot as this will burn the tin and make the copper unfit for use without retinning. Some mechanics prefer to file the copper while it is hot but the writer files his cold. The sides of the point should be filed as flat as possible and the edges should be smoothed so they are not sharp.
One way to tin a copper would be to heat it after cleaning until the cleaned surface begins to show color. As soon as this coloring which is really oxide appears touch the surface with rosin-core solder. The rosin will immediately remove the oxide and the solder will fuse to the surface. The point will now be the color of tin instead of copper. It must be remembered that if more heat is applied after the surface begins to show color the oxide will be so heavy that the rosin will not remove it. This has been mentioned before under Fluxes. All four sides of the point should be tinned except for certain work for which only one side is tinned. This will be explained later.
Another method for tinning would be to heat the copper until it just begins to melt a bar of solder. Remove the copper from the fire and touch one side with tallow candle and follow this immediately with solder which will tin the surface. Continue until all four sides are tinned.
Another method is with the use of a brick. An ordinary building brick is hollowed slightly on one side. Into this hollow melt a little solder and some rosin. Take the copper after it has been cleaned and heat it until it will just melt solder. Take it from the fire and gently rub the copper in the solder and rosin rolling it so all four sides will tin.
Still another way to tin the copper is with the use of sal-ammoniac. The copper is cleaned as before but must be hotter than for other flux. If it is heated over an open flame, by rolling it in the fire colors will be seen to run on the whole copper. It is then hot enough. Or the copper can be rubbed on the sal-ammoniac and if heavy smoke rises it is hot enough. Of course it must be borne in mind that at no time in tinning should the copper be red hot. Melt a little solder on the sal-ammoniac and keep rubbing the copper on the surface until it is tinned. When the copper has been tinned by any of these methods wipe any excess solder off the point with a piece of cloth or a brush. After the copper has been used for a while the point may need to be touched up again on the sal-ammoniac. When it becomes badly pitted and black it should be filed over again and retinned.