A Thin Line: Capillary Action In Soldering


There is a very important rule of physics that applies to all liquids, including solder: When it contacts with solids, liquids are drawn into small spaces with capillary action. The result of adhesion, cohesion, and surface tension, this same force jepls squeeze the blood through the finest capillaries in our bodies, hence the name.

Understanding how this principle applies to jewelry work can be helpful. When soldering a long seem, you want to solder to fill it in evenly and completely. For this to be accomplished, a few conditions need to be met: The metal and solder must be clean, fluxed, and heated to the flow temperature on the solder. If those conditions exist, the solder will travel from one end of the seam to the other, following the heat of the torch.

This phenomenon is particularly important when you are soldering tubing. As the flux liquifies, introduce solder at the end of the seam. Drawn by the heat, the liquid will squeeze through the seam with capillary action. Continue heating and add solder farther along the seam as needed, until the seam fills.