Hot and Soldered

It would seem a simple matter to join metal to metal. However success in gold soldering involves more than meets the eye. When doing short runs, you must follow a few fundamental procedures to ensure a neat, strong, and uniform joint.

Fitting. The strongest joints are produced with the closest-fitting pieces, so make sure the surfaces are smooth, free from burrs, and fit tightly. For sizing rings, start by sawing an appropriate size piece out of the shank, Most ring mandrels have a gauge for measuring the difference between finger sizes; the difference equals 2.54 mm per size. Push the shank together and saw the seam one more time. This will create two perfectly matched ends. Even if the saw cut is slightly crooked, both sides are cut simultaneously, so the seam is still symmetrical.

Cleaning. Parts must be thoroughly cleaned. Both joint and solder must be free of dirt, marker, saw wax, finger oils, tape, pickle, buffing compound, etc. Any dirt near the joint will prevent the flow of the solder.

Fluxing. Cover the entire joint with flux to protect the metal against oxidation, thereby aiding the flow of the solder. To reduce the amount of cleaning needed after soldering, firecoat the entire piece with boric acid and alcohol. (If you use Battern’s flux, do not use a hot flame; it will burn off the flux.)

Jigging. Clamp, or jig, the piece to secure proper alignment and prevent movement of parts during heating. Use the lightest material possible and have the least amount of contact between jig and piece; this will keep the jig from acting as a heat sink. The jig should also be made of a material that does not conduct heat well-not copper or aluminum!

Heating. Solder flows toward heat, so whenever possible, position the torch to draw solder through the joint. Using a soft flame, slowly and uniformly heat the joint and surrounding metal before flowing the solder: Continue heating until the joint shows a dull red color then concentrate the flame along the joint. The color of the joint is a guide to the temperature in soldering (see chart), so be careful not to let changes in lighting affect your judgment.
Metal Color

Approximate Temperature
First Visible Red

900 F
Cherry Red

1,400 F
Dull Red

1,200 F
Bright Salmon Red

1,600 F

Do not let the material reach a bright salmon red!

Remember, let the heat of the parts being joined control the solder’s flow; do not flow the solder with the flame of the torch. Other factors to consider during heating:
* When joining metals of different thicknesses, preheat the heavier piece to avoid overheating the smaller piece. This rule is very important when soldering a setting to a shank
* When soldering an enclosed object, such as a bead, provide an escape for steam and gases trapped inside. The gases will expand rapidly and, unless vented, could cause the piece to explode.
* Many gold solders contain zinc, which will burn off as a vapor and change the proportion of the alloy. As a result, each time solder becomes fluid, its melting point rises. Overheating a previously soldered joint will burn out the zinc and could leave a pitted seam.

Soldering. Using the correct solder is crucial. When assembling a piece, use a solder with as high a melting temperature as possible, preferably plumb gold hard solder: This will enable you the necessary platinum {remembering your 2.54 mm rule). You close the gap, again leaving only a small space, and cut both ends so they match perfectly; the seam should be no bigger than a hairline crack. Next, you choose a 19k or 20k weld white gold solder, which has a color and strength similar to platinum’s. Rolling a thin strip that’s smaller than the cross section of the ring, you wedge it into the gap and apply pressure to the shank, creating tension against the solder so the two ends bond better. Using a reducing flame, you melt the solder {with this method, you don’t have to worry about overflow). Finally, with a tungsten burnisher, you bright-burnish the area; this will compact the platinum surface and remove all traces of the seam. Since gold polishes faster, you pre-polish all the platinum portions of the sizing area to guarantee an even finish.

Two down, one to go. You pick up the cocktail ring-a semi-mount with baguettes running down both sides of the shank. You frown. If the diamonds had been set only on the top, you could have used the platinum technique–either welding or applying platinum solder. Since platinum doesn’t conduct heat well, you’d have had no problems as long as you used a very fast, hot oxidizing flame, kept direct flame away from the diamonds, and protected the stones with either a cooling gel or water. But the baguettes pose an obstacle; since no stone-diamonds included-can withstand the temperatures necessary for either welding or the use of platinum solder.

You have a choice: Either remove the stones and apply the platinum technique, or keep the stones in place and use gold solder. You opt for the easier route and
keep the stones intact. Following the same steps as with the bi-metal ring, you’re done in no time at all.

You sit back, the three rings in front of you, and pat yourself on the back for a job well done. Going back to your job box, you notice another sizing order-another platinum wedding band, this one with diamonds encircling it. You’re pulse doesn’t quicken one beat.
You’re ready.

AJM October 1999

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