Testing materials for flux…

by Jamie Hall on February 26, 2010

This isn’t very scientific, but I may repeat and/or expand this test. All examples given here were done with small sterling silver rings and Cookson’s easy silver solder wire, using a small oxy-hydrogen flame. The solder is cadmium free. Each example has the material in BOLD, followed by a description of the effect.

Having tested more materials, I am concerned about variation in my materials and method – for those materials that seem to be effective, I’ll eventually try testing them under more controlled conditions.

NO FLUX – Very poor result. Metal was partially melted before the solder ran through, and only 50% of the join was filled.

AUFLUX – Very good result. Light glass residue.

BORAX POWDER – Good result. Heavy glass residue.

BORAX + WATER PASTE – Good result. Less glass residue due to more precise placing of paste.

BORAX + BEESWAX – Good result (surprised me), only slight residue of glass due to low quantity of borax.

BORIC ACID POWDER – Very good result. Heavy glass residue. Definite red/orange colour to the glass with all boric acid tests.

BORIC ACID + WATER PASTE – Average result. Heavy glass residue. Slight surface melting on the silver, but that may be my error.

BORIC ACID + BEESWAX – Good Result. Light glass residue.

BEESWAX – Poor result, but much better than using no flux at all. Join was poor, but metal didn’t melt.

SHELLAC (FLAKE/POWDER/+WATER/+BEESWAX) – Very poor in all cases. It was not possible to make a compound with beeswax, and neither was it possible to mix it with water, as it is insoluble. When the water was heated, it yielded a transparent scum, which was collected and tested, but had the same characteristics as the shellac. The silver ring was melted in all cases.

CUTTLEBONE (POWDER/+WATER/+BEESWAX) – Appears to be a potent anti-flux – this is either due to the high calcium carbonate content of cuttlebone, or it might just be that most things work that way – that’s why I want to try dirt, and see if that has the same effect.

CHARCOAL (POWDER/+WATER/+BEESWAX) – Very poor result, usually resulting in a melted ring before solder flowed. As with cuttlebone, this may be acting as an anti-flux, or it may be making the metal surfaces too contaminated. The powder wouldn’t mix with water properly, and left a layer of “skin” on the surface. This seems like an interesting property which might be used to coat objects with charcoal, should it be necessary.

ROSIN (POWDER/+WATER/+BEESWAX) – Very poor result, usually resulting in a melted ring before solder flowed. Rosin, also known as colophony, is used as a flux for lead-based solders, but the temperatures I am using are clearly too high for it, and it burns leaving a dark residue behind.

Summary: I’ve always been told that greasy joins are bad for soldering, so I’m baffled that beeswax doesn’t ruin the work. But, seeing how it improved the effects of borax (ie. less glass residue), it may be worth trying it with other substances, particularly if they are only available in small amounts – barely any borax was needed to get a result. Hopefully I’ll update this post at a later date, with more substances.

Things to try:

  • Gum tragacanth
  • Coke dust
  • Table salt
  • Dirt (depends on the dirt, though…)
  • Charcoal Ash – this was difficult to produce at the bench, so I’ll wait until I’ve got my furnace ready.
  • Potash
  • Lye
  • Cream of Tartar
  • Natron


Richard Sewell February 28, 2010 at 09:58

Your post got me wondering how much was known about historical solder and fluxes. I had a bit of a google, and although I didn’t find a very clear answer I did come across some references you might be interested in. If you haven’t seen them already, of course.

Take a look at this thread:
and thsi post in particular:

Kerri Duncan February 28, 2010 at 15:17

Jamie- cool experiments- just a question- were you using plain borax or boric acid? I have seen some older jewelers using wax and dust coke (coal ready for forge use- sometimes called “breeze”)… just curious.

Jamie Hall February 28, 2010 at 17:59

Richard – those posts were interesting, thanks. I want to try building a ceramic bunsen burner now – whether or not there is evidence for them!

Kerri – I was using commercial borax for household cleaning. But you’ve reminded me that I have some boric acid in the cupboards, so I’ll try that using the same methods.

Do you know which waxes were used with coke? I’ve seen tallow mentioned a few times in other processes.

shelbyvision March 1, 2010 at 16:21

Interesting stuff. I would call it the Edison method. Thomas Edison was not a scientist, but a relentless experimenter who would try everything imaginable until he found something that worked. Virtually everything he invented was the result of a series of happy accidents.

Jamie Hall March 1, 2010 at 16:50

I’m open to other imaginable substances, if you can suggest any.

Hmmm…was Edison the first of the modern inventors, or the last of the old polymaths? Invention by experimentation must have always existed, but depended on people with the wealth and freedom to mess around with things. I could have done these simple tests at any time in the past 5 years, but I never did.

Jamie Hall March 2, 2010 at 19:05


Kerri Duncan March 8, 2010 at 15:19

Jamie- the waxes I have encountered are the sealing wax used for wine/whiskey bottles- and a more brittle wax that has been used for sealing letters. As well- the Boric Acid you can buy from a supplier- but most common roach powders are 99% boric acid as well… potentially a cheaper alternative than buying from Grobet/Cooksons/Rio. When mixed with denatured alcohol it forms a bluish slurry that performs well from a more frugal standpoint- but can leave a bit more glassy residue which need s more pickle time to dissolve. If you are in the UK I do not know about your suppliers but I can buy a 6 ounce bottle of “Roach Powder” for 3.50 USD from Lowes or Home Depot that will last a good while. Email me for more info if you would like- I am enjoying your experimentation.

Jamie Hall March 9, 2010 at 08:54

The wax you are describing sounds like shellac (see above), or shellac-based materials. Stone setters often use shellac to fix small settings in place. Shellac itself wasn’t effective, but it’s looking as if waxes and oils simply allow better placement of materials than their powder and paste forms.

Denatured alcohol is usually called methylated spirits, and is purple over here. I’ve not tried using as a mixture with these materials, but I ought to. I’ve used meths and boric acid to protect against firestain before, although I’m not convinced that it works well. I’ll have to see how well it fluxes instead.

That sets me thinking about how pure the Vikings could get their ethanol? Would it have had use as a solvent? Does strong whiskey (or another spirit) work?

Kerri Duncan March 16, 2010 at 12:47

The food-grade wax for sealing the bottles does not contain any shellac- just a highly refined wax- doesnt get hard like shellac (you can always indent it with a fingernail) and it doesnt chip till it gets cold. Liked the book and the postings about the bronze-age skill-set… Hope all is good- and keep creating!

Kerri Duncan March 16, 2010 at 12:56

The distillation of spirits can be achieved through natural fermentation only to about 18-22% (but not in the viking time as this is a champagne specific cultured-yeast of less than 200 years of production.) The norm was about 12% peak as at this point most open-fermentation bacteria have created an environment in the solution it becomes hard to live (remember alcohol is the bacterial WASTE- they toxified their environment)
-One way of concentrating the alcohol in the periods before Wines and Meads were at the peak was to let the casks and kegs freeze- water and alcohol do mix readily- but the water water and pulp mix would freeze, and the alcohol and some water would not- this could yeild up to a 25% alcohol solution- but they didnt know this- and probably didnt care either… The use of mash pots and distilation columns (stills) didnt start until after the Viking ages… Hope this wasnt too much info- be safe and have a great day!

Greg November 25, 2010 at 20:40

I have in the past used baking soda-left a dimply coating to the silver in contact with the bottom of mold.

I have used no fl;ux with very clean scrap silver-silver looked good but did notpour well.

I read you variatins with beeswax, I have an endless supply of beeswax so if you find a recipe that uses beeswax I want to know.

I am melting silver now and remembered I have some roach powder (boric acid), but I hear that boric acid reacts with the graphite in the crucible? Still may try it once with good ventilation.


Jamie Hall November 26, 2010 at 23:43

I tend to use white ceramic crucibles, so I hadn’t heard the problem with graphite and boric acid – it might be best to steer clear of it.

Eduardo April 11, 2011 at 23:03

Try with kerosene?
I have a good experience with making Damascus steel (with ferrous metals)
Kerosene + borax?
Sorry for my poor english

Jamie Hall April 12, 2011 at 07:57

Is the kerosene fluxing or cleaning? I suppose that any flammable material will leave a layer of carbon-rich material on the metal, which might be enough to act as flux. Might take something heavier than kerosense, though.

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