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Fluxes for Soldering silver.

Updated: Feb 20, 2022


I’ve tried many fluxes from liquids to pastes. The problem with them is that they all contain water. This has always given me problems when soldering small parts because when the heat is applied the water boils causing parts to move. I’ll still use paste flux like Handy Flux on larger pieces of jewelry. The other problem I’ve experienced is that it doesn’t prevent fire scale as good as I’d like. One thing it can do is to indicate if your piece is free from contamination. If the flux repels and doesn’t want to cover, it’s indicating there’s contamination or oil on the surface of the metal.


I have found that using a mixture of “Powdered” Boric Acid and Denatured alcohol is the best product to use. This is what I use 95% of the time. It’s a very good combination flux and fire scale prevention. You must use Denatured Alcohol and “Powdered” Boric Acid. There is no substitute that I have found that works. One problem finding Denatured Alcohol, it’s not sold in all States.


The ratio of the mixture is not that critical. Some people say to mix it 50/50 but that’s not true. If you add too much Boric Acid, it just doesn’t dissolve into solution.


Safety:

Always have a fire extinguisher handy.

Alcohol is flammable, cover it in your air tight container before you ignite your torch.

If you ignite your container of flux, Stay calm and replace the cover to extinguish the flame.

When I'm teaching an apprentice, I have them ignite the flux and cover it to show them that they have control over the situation. Having them do this teaches them not to over react and how to work safe.


Application.

You can dip, apply with a brush or even spray with a pump bottle. To spray it on, I warn the piece before I apply it. This is the best way to build up the amount of flux on the surface. When you heat it the Boric Acid it melts forming a clear glaze over the entire piece. This Boric glaze coat is the complete shield that protects the metal from oxidation.


Other tip to save work is to prep all your pieces before you solder them.

The preparation that I do is to sand all surfaces with a Tropical Shine 400/600 fine pink cushion file and polish some areas that I won’t be able to reach after the assembly.


Pickle:

The purpose of pickling metal is to dissolve and remove the copper from the surface of the sterling silver. Sterling silver is an alloy of 925 parts pure silver and 75 parts pure copper. The copper causes the black oxidation on silver jewelry. When soldering, the heat with excessive free oxygen causes the copper to oxidize causing the fire scale.


The best and most economical pickle solution I’ve found to use is a product referred to as PH Down. You can find the product at any pool of building supply. This pickle has no odor and works extremely well when hot. You can also super charge the pickle solution by adding Hydrogen Peroxide. If you do this it will rapidly deplete the strength of the pickle and will need to be discarded.


Some tines I will pickle to deplete the surface copper and rinse the parts the parts before I solder them. Then I will pickle the completed piece of jewelry and tumble it. The reason is I want the piece to have less oxidation and stay bright longer.

More about this and different finishing techniques in a future blog.

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