Solder paste is a mix of powdered metals suspended in a paste made from flux. Flux will help the solder flow, as well as keep oxidation on the jumpring to a minimum. To use solder paste for closing jumprings, make sure the jumpring is closed so the ends are flush. Also make sure the jumpring is clean. Place the jumpring onto a charcoal block or soldering board. Apply a bit of solder paste to the joint. Heat the entire jumpring with the torch then focus the heat on the joint, below the area where the paste is resting. Solder is drawn to the heat so by heating below, the paste will draw the solder into the joint.
If needed, place the jumpring into a bath of pickle prepared in a pickle pot; pickle will remove any oxides on the surface of the metal. You can also polish the surface using polishing papers (400-1200 grit).
Solder-filled jumprings are a great alternative and also require the use of a torch. To solder a solder-filled jumpring, make sure it is closed so the ends meet and are flush. Place the jumpring onto a soldering board or charcoal block. Heat the entire ring with the torch then focus the heat on the joint. Watch for the "flash" of solder then immediately pull the torch away. Overheating will cause the solder to pull back into the wire, or worse, melt your ring.
Use of a torch requires the proper safety equipment, tools, supplies and plenty of practice.
Another option to securely close a jumpring is to use Loctite® 454 Gel adhesive. Loctite 454 Gel adhesive works well for this application as it adheres to smooth surfaces, fills in gaps, cures in seconds and dries clear. Be sure to use jumprings that have clean ends that close flush.
- Michelle Wood, Jewelry-Making Expert