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.
Before leaving the soldering copper there is one more very important subject which should be taken up. The craftsman is often called on to do a soldering job which has been done before. It very often proves to be a job which was done carelessly or by one not experienced with the use of a soldering copper. It may be a place that has had too much solder piled up on it which has covered some untinned spots. This is not always the case as sometimes it may be in a position where it is subjected to more or less vibration which has finally broken the joint. In making such a repair the proper thing to do is to remove all the old solder.
Included in the kit recommended will be found listed a small paint brush. It should have quite stiff bristles. This brush is used for brushing molten solder. Discarded tooth brushes can be used for this purpose. The hot copper is rested on the spot to be cleaned. When the old solder melts remove the copper and quickly follow the copper, and brush the solder off before it has time to solidify. If it is not all removed with the first heat it will have to be heated and brushed again until it is all cleaned off. This cleaning will expose any places that were not tinned. These can now be cleaned and the soldering job can be completed. This same method can be used for coating metals with solder. The metal is tinned in the usual way and while the solder is still melted all surplus solder is cleaned off with a brush or piece of cloth. There are times when copper or brass are used for repairing parts that are made of white metal or plated with nickel or chrome. By this method the copper or brass may be tinned to match the rest of the job. This tinning or plating can be done with a flame but this must be done carefully as there is danger of over heating.