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Soldering Help Needed - Issue with Borax

Hello! Wondering if anyone can shed some light on an issue i’m having while soldering.

I use a Boric Acid Powder/denatured alcohol mix prior to soldering, with a paint brush applicator. The solution clumps just as it hits the metal.

I use a butane torch to heat it, it bubble and becomes dark and sticky, dirtying the joint. Then my solder doesn’t flow properly.

I work in a garage for now, in Toronto so the weather is colder. Is environment temperature an issue? Is it the Borax mixture?

Any help would be great. Thank you.

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I use boric acid and denatured alcohol in a pickle jar with a wide mouth and keep adding alcohol when it evaporates (always put the lid on after dipping your item). Make sure you stir it so it is thoroughly mixed and then quickly dip your piece and hold it over the jar to drain off. I find that will protect the silver but I also use paste Handy Flux and apply it to the piece where I am going to add my solder chips so they stay in place while I heat the piece up. I hope this helps.

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Boric acid and alcohol is more often used as a barrier than as a flux for the joint. It is commonly used to protect diamonds from burning and prepolished parts of a piece from oxidizing while soldering. To apply boric acid as a barrier, mix it with alcohol, dip the piece while it is cold, then set a flame to it and let the alcohol burn off. This will coat the piece in a film of boric acid.
A paste of borax and water is more generally used to flux the joint. Handy Flux is basically borax and water with some other additives. If you want to go old school get a borax cone and a slate and grind it to a paste with distilled water, rather like grinding Chinese or Japanese ink sticks.
Or use one of the commercially prepared, bottled fluxes. Which is best depends to an extent on which metals you usually work with.


I lifted the following from a previous Orchid comment by James Binnion. He makes the point that boric acid and alcohol is a firecoat and soldering fluxes contain borax.

“Also as I am sure you know but for the record neither boric acid and
alcohol or Prip’s are soldering fluxes they are fire-coats. They
provide protection from oxidation on the rest of the piece while
soldering, you need to use a soldering flux at the area(s) you are
joining. Many soldering fluxes like Batterns and Handy Flux have
borax as the main component but they also have other compounds like
chlorides, fluorides and carbonates added to both reduce the
temperature that the fluxing action takes place at and to help in
dissolving the more difficult oxides (like the silicon dioxide
referred to in recent posts). A lot more on fluxes ant
their formulations and actions is available in Brepohl’s “Theory and
Practice of Goldsmithing”.”


A borax and alcohol suspension is a good barrier flux to keep the entire piece from developing fire scale, especially on prepolished parts when doing a final soldering or annealing operation. It isn’t a good joint flux. You need one of the reliably available fluxes that are specific to this purpose. I use Handiflux. I apply it, then boil it off prior to placing a solder pallion(s). The boiling flux may displace the pallion(s) if you don’t boil it off first just when you want to apply the heat. I keep my borax and alcohol suspension in a wide mouthed mason jar with a spring clip lock. I put the pieces to be coated into the jar, give it a shake, take the pieces out, give them a shake, seal the jar (very important), then light my torch. You don’t want to set a jar of alcohol and borax on fire. I have done it. Then slowly burn off the alcohol leaving a nice white deposit of borax and then solder your joint. Give the piece a good soak in rinse water after pickling it to remove any glassy flux deposits. They are very hard to remove otherwise, then finish your piece. Good luck…Rob


This has been very helpful. Thank you all.

I always used methanol since it is a far better solvent for boric acid (and borax) than ethanol or denatured alcohol. It is also far cheaper; and more toxic. The latter wasn’t a problem for me since I used good ventilation and was very wary of spills or skin contact.
As pointed out in previous posts, boric acid in alcoholic solvent doesn’t make a good soldering flux but is very good for protecting other heated areas from oxidation.

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Thanks for the pointer of heating the Handiflux BEFORE adding your solder. I have to chase them from time to time!