Saturday, October 4, 2008

Torch Soldering vs. Soldering Iron

There are several posts on my blog regarding making soldered glass slide and pebble jewelry. That application calls for using a soldering iron, like those used for connecting pieces of stained glass. The basic elements of that method of soldering apply to torch soldering as well.... metal-to-metal contact, the use of flux to flow the solder, the use of solder & a heating tool that reaches the temperature that is necessary to melt the solder. But the methods are not necessarily interchangeable. For example, you cannot use torch soldering to make the glass slide pendants. The heated area is too broad and too hot. The copper tape & paper artwork would melt and the glass would shatter. But the torch method is the best choice for heat connecting precious metals like silver. A soldering iron tip must be touching the solder to melt it and therefore, it would get in the way when trying to make the small unnoticeable connections that are desired for finer jewelry, whereas the torch only needs to be in proximity to the area of connection to form a heat source that will melt the solder and draw the molten liquid to it. The torch is hot enough to melt solder with a higher precious metal content than the soldering iron generally, so for that reason it is preferred for fine jewelry as well.

There are a few pre and post solder steps that are required when torch soldering silver. When silver (other than pure fine silver or argentium silver) is exposed to high heat, it gets something that is called "Fire Scale" which totally discolors the silver and it is very difficult to remove because it goes deep into the metal. This happens because of the copper content that is alloyed in sterling silver. For this reason, I work with fine silver only, but sometimes the strength of sterling is necessary.

To avoid fire scale, you can prepare the pieces of silver by soaking them in a prep solution designed specifically to address fire scale. Also, some people lay the silver on a chunk of natural charcoal (not BBQ charcoal!) when soldering to help absorb oxygen which is in part to blame for fire scale.

I found this information in the Art Jewelry Mag forum by "bleugurl" but I have not personally verified it:
"To prevent fire scale, stop oxygen from getting in contact with the metal. Fire scale is formed whenever silver and sterling is heated above about 1000 degrees F. Oxygen combines with copper to form cuprous oxide which exhibits as firescale.

Prips Flux, denatured alcohol/borax solution, Cupronil…any of these products will work. You might try coating the whole piece in flux before soldering. Be generous with the flux. To properly apply anti-firescale-fluxes, the metal must be heated slightly. Paint, dip the piece or spray on the anti-fs-flux. A mist atomizer bottle works well here. If the metal temperature is correct a white grainy coating will form. Quickly play a flame across the wet fluxed metal to dry it. This will evaporate the alcohol, leaving a white coating of tiny borax crystals."

After soldering, the piece must be pickled to clean all of the residue and flux from it.

This video created by demonstrates how to coat your pieces with prep solution and some handy tricks for soldering small parts like jump rings with a torch. Check it out. I hope it helps you as much as it helped me.

Here is another video demonstrating another method for coating with flux & torch soldering on a piece of charcoal:

Happy soldering!

No comments: