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.
A copper must be tinned so it will carry a small body of molten solder in which the object to be soldered is partly submerged or flooded. This flooding is the medium by which the heat is conveyed to the object to be soldered on account of the close contact made by the hot solder. If an untinned copper is held against a piece of work it will not heat it because the contact is not close enough. In soldering the work must be heated to the temperature of the solder as it leaves the copper. For ordinary work the soldering copper is tinned on all four sides. It will be noticed that a little solder melted on the upper side of the point will soon run to the bottom and hang in the form of a drop. Therefore when soldering splices on wire or any work where the copper is held under the object to be soldered only one side of the copper is tinned. Tinning only one side will allow a little solder to pile or hill up on the top. The other sides not being tinned will not allow the solder to run to the bottom.
There are many ways to heat a soldering copper. The gasoline or kerosene furnace, gasoline or kerosene blow torch, gas flame, forge, coal fire and the old style tinner's charcoal fire pot. The flame used for sweating work or heating soldering coppers should be blue. The flame of a torch or gas burner shows two colors. A light blue cone will be seen at the end of the mixing tube and outside of this is a darker blue. The hottest point of the flame is just beyond the light blue cone. This cone does not give off any heat. It should be remembered that the work should be held so it receives the flame just beyond this non-heating light blue cone. The yellow illuminating flame is not suitable as it covers the work or copper with soot or lamp black. There is very little heat to a yellow flame. When using a forge or other coal fire it is best not to put the copper directly in the fire as the tin burns off the point very easily. To prevent this place a piece of 11/4" iron pipe about 8" long into the fire and heat the copper inside this pipe.
The gas flame is the most easily regulated heat. It can be turned down so it will keep the copper at just the proper heat. It pays to watch the copper while it is heating because it is not a very pleasant feeling to reach for it and as the experienced tinsmith says, "find a goldfish." It means retinning the copper when this happens. An electric copper can overheat as well as an externally heated one if the current is left on when it is not being used continually. When the tin on the point begins to take on a lead gray color the current should be turned off to allow it to cool a little.
All soldering is not done with the soldering copper. Some tinning is done by applying a flame directly to the work. This tinning is done in just the same way as a soldering copper is tinned. The work is heated until it will melt solder at which time flux is applied followed by solder. The most common means for heating without the soldering copper are the Bunsen burner, acetylene gas torch, electricians alcohol torch and a gasoline or kerosene blow torch. Figure 26 shows how the Bunsen burner may be changed so it can be used for this tinning.