Silver Soldering

By David Nelson

Silver solder is primarily used by silversmiths and jewelers but is an ideal method for model builders to join metal parts made of brass or steel. The joint created is stronger that the metal parts being soldered thus eliminating any fear of breakage.

Silver solder is an alloy consisting of Silver (AG), Copper (CU) and Zinc (ZN). In addition, the ones with a lowest melting points may contain Tin (SN) or Cadmium (CD).

Also available are “Silver Bearing” solders which are soft solders with about 5% silver content. They melt at 400 degrees and should NOT be considered a silver solder.

The silver content determines the hardness and melting point of solder types. The chemical composition of commonly available silver solders and their melting points are:

Name / AG / CU / ZN / CD / Melts at C / Melts at F
Hard / 75 / 22 / 3 / 773 / 1425
Medium / 70 / 20 / 10 / 747 / 1390
Easy / 65 / 20 / 15 / 711 / 1325
Easy Flo / 50 / 15 / 15 / 20 / 681 / 1270

The solders are most often referred to by the name but in some cases by the silver content percentage.

When soldering two pieces together any type of solder can be used but typically you would use Easy or Easy Flo because of the lower melting points. If soldering multiple pieces together use a harder solder for the first joint then solders of decreasing hardness for the subsequent joints. This allows the solder in the initial joints to remain solidified while the later joints are soldered.

A note of caution: Cadmium gives of a toxic gas when melted so Easy Flo solder should only be used in a well ventilated area.

Silver solder comes in three forms which allows you to select the one best suited to your need.

  • Paste: The paste consists of a flux impregnated with solder. It is ideal for situations where you need to use a limited amount of solder. An example would be sealing the loop of an eye bolt.
  • Wire: It comes in various diameters and works well for most soldering.
  • Sheets: Sheets come in various thicknesses. They work well for soldering pieces which have a larger, flat area to be joined. They can also be cut into small pieces when a limited amount of solder is required.

Silver solder is available in Toronto from H&W Perrin at 90 Thorncliffe Park Drive. Their web site does not contain their full product line so if you don’t see what you want, phone them.

The essentials for Success.

There are four things that must exist to make your silver soldering successful.

  1. Clean the metal of any oxidization, oil or grease. If soldering stainless steel and it gets over heated a black oxide will form on it’s surface and your solder will not adhere to it.
  2. Get a good mechanical fit between the pieces being soldered. Silver solder will not fill gaps.
  3. Use a torch that generates sufficient heat to bring the metal to the melting temperature of the solder. If the metal is not at the proper temperature the solder will melt in the heat of the flame but will just sit as a blob on the metal’s surface. When the metal is at or above the solder’s melting point the solder will flow like water.
  4. Use the proper flux. This is a must. “Handy Flux” made by “Lucas-Milaupt” and available from “Praxair” works well. This flux is water soluble so if it starts to stiffen up in the container just mix in a little water and it will be pliable again.

Soldering

  1. Prepare your material and ensure there is a good mechanical fit between the parts.
  2. Use clamps or some other means to secure the parts so they cannot move while the solder is being applied. Clamps should be far enough away from the joint so they do not absorb heat you want applied to the metal. If using wire to hold the pieces be sure it is a material that the solder will not adhere to such as tungsten. The work piece must be placed on a fire proof board.
  3. Apply flux over and around the joint. For larger pieces flux can be placed between the parts and the excess squeezed out when clamping.
  4. Heat the parts. The flux will melt and become clear as the metal nears the melting point of the solder. Continue to apply heat then touch the solder to the metal to see if it melts or let a drop of solder fall on the metal. Once everything is hot enough the solder will flow around and into the seam between the parts.
  5. Allow the soldered piece to cool then place it into a pickle solution of one cup of vinegar and one tablespoon of salt. The pickle will softer the flux remaining on your work and allow it to be scraped off. Use a knife or file to clean off all flux and file off excess solder. Then, use a wire wheel and buff wheels to polish the piece.