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The Asimi Art Digest shares articles about techniques of making jewelry. In this post, we explain soldering and when you should use which solder.

What is Soldering?

Soldering is a process that joins two pieces of metal together by heating a third metal, which has a low melting point (known as solder), until that metal melts and then forces into the space between the metal pieces being soldered together. When the solder solidifies, a bond is created between the pieces of metal that is as strong as the metal it connects.

Soldering is generally classified into two divisions: hard and soft. On objects which require soldered pieces, use a hard flow first and then an easier flow. However, easy flow solder alone can be used for making most simple jewelry if the seam is not visible.

Hard soldering

This is done with strong, high melting silver, gold or platinum solders. Most pieces of precious metal are sold together with hard solders.

 

Soft soldering

Done with a comparatively weak, low melting, tin-lead alloy solder. Soft solders are used when some parts of the pieces will not stand the heat of hard soldering, e.g. enamels, certain findings and some gemstones.

 

In both hard and soft soldering, there are certain rules that must be adhered to:

  • All metal surfaces to be soldered must be free from dirt and grease.
  • The surface to be soldered together and the solder must be coated with flux.
  • The proper solder must be used.
  • The surface of the metal to be soldered together must be shaped and then positioned so that they fit together perfectly, and they must be held together without tension.
  • The solder must be correctly positioned on the metal.
  • The amount of the heat must be regulated; from the torch, through the metal and to the solder.
  • The solder must flow and cross the joint in order to successfully join the pieces of metal together.

Flux: the anti-oxide hero 

Most metals oxidise (turn black) when heated. The oxide prevents the solder from adhering and flowing. The flux facilitates the adherence and flow of the soldering by several ways:

1. Forming a protective film to keep the air away from the metal. When heated in air, metal forms a surface ‘skin’ called oxide that inhibits the flow of the solder.

2. Dissolving small amounts of oxide that have formed.

3. Wetting and lowering the surface tension of the metal.

Types of solder hardness

 

There are three main grades of solder used for soldering—easy, medium and hard. Easy solder melts at the lowest temperature, medium solder requires more heat to melt it, and hard solder requires further heat to melt it.

Always match the solder to the metal being joined! Thus, when soldering gold, match the solder to the carat and colour of the gold. For example, if you were to solder 9 carat yellow gold, then use 9 carat yellow gold solder; solder 18 carat white gold with 18 carat white gold solder, and so on. Silver solder also solders copper, gilding metal and brass.

Silver solder, an alloy of silver, copper and zinc, is the solder used for silver jewelry and copper, brass, bronze, gilding metal and nickel silver objects, when very strong joints are required. The melting point of the solder depends upon the percentage of zinc: as the percentage of zinc increases, the melting point of the solder decreases.

 

This chart sums up the different hardnesses and their metal percentages:

Solder Silver % Copper % Zinc% Melting Point °C
Hardest 82 14 4
Enamelling 77 17 6 800
Hard 75 22 3 778
Medium 70 20 10 765
Easy 65 20 15 723

We hope that this article shed some light on the soldering process and basics for you. If you enjoyed this post, please leave a comment below!

 

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