Brazing Silver Soldering and Soft Soldering
These three processes all have similarities when they are carried out. They all require the parts to be joined to be very clean before joining is attempted.  They all require a flux (usually Borax in the case of brazing and silver soldering and Zinc Chloride or Resin in the case of soft soldering) which is a chemical that works to keep the joints clean whilst the job is being heated and to make the solder flow once it has melted. Soldering will not be successful if flux is not used. Brazing and silver soldering joints are heated using a gas torch. With these three processes the work itself is not melted. An alloy is used to 'stick' the pieces together. Welding requires the work piece to be melted.

Soft soldering done with the type of irons shown is weak in comparison to brazing and silver soldering. The solder is largely made of lead and tin mixed together. The most common materials which are soft soldered are copper, steel brass and tinplate.

The brazing torch is also used for silver soldering. It provides a strong joint. The solder for brazing is called spelter  and is made largely of copper and zinc. Silver soldering spelter is largely silver copper and zinc. Main metals joined using these processes are steel ,copper (brazing), steel, copper brass for silver soldering.

Brazing and Silver Soldering ( Temperature range - 625 to 875 degrees C)

Stages in Brazing/Silver Soldering
1 Joints need to be cleaned using emery or file.
2 Mix flux with water to obtain a look of melted ice cream.
3 Put flux on the joint and on the spelter.
4 Hold the joint in place with wire if necessary.
5 Heat the work to the correct temperature (625 degrees is dull red 875 degrees is orange/red).
6 Touch the spelter on the joint when BOTH  pieces are hot enough, the flux will make the spelter flow.
7 Allow the joint to cool.
NB If both parts of the work are not equally hot the spelter will stick to the hottest part and the joint will not work.

Soft Soldering (approximate temperature 200 degrees C)
This is done with either an electric or gas heated soldering iron. The iron has a copper tip which carries heat and solder from the gas/electric to the work surfaces. The soldering iron tip needs to be charged with solder after heating this is done by dipping the iron tip into flux and melting solder onto it.

Stages in soft soldering
1 The joint must be clean and fit well together since soft solder does not fill gaps very well.
2 Place flux on the joint. (Active fluxes are better for most jobs as  they provide a better final result but do give rise to corrosion after soldering and for this reason the joint should be well washed afterwards). (Passive fluxes are used in situations where the joint cannot be cleaned after soldering e.g. Electrical work).
3 The surfaces to be joined are coated with a thin film of solder (called tinning) using a soldering iron. The job has to be warm enough to allow the solder to flow from the soldering iron to the work surface.
4. After tinning the job is reheated with a clean soldering iron to melt the tinned surfaces together. Wash the work if active flux has been used.