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The Absolute Last Final Word on Anhydrous Borax Flux

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32 minutes ago, anvil said:

My initial reaction to charcoal is,,, found it on the internet, you say? No judgement, just my initial reaction til there is more information.

The original discussion was here:


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17 hours ago, Frosty said:

I ran some charcoal through the shop blender and collected maybe 1/8tsp of dust and mixed it with about 1/4c of Petersons. I'm thinking it was too much but that worked and I haven't used that test batch up so I haven't tried a different ratio.

Tristan, AKA Teenylittlemetalguy on IFI was playing with it more than I was. We haven't talked about it in a while.

Frosty The Lucky.

I honestly have not fire welded much recently. I played with the ratio a bit and found I could lower the charcoal dust percentage and still have it work well. It worked very well for welding leaf spring to itself, which is typically really hard to do.  Give it a try, just make sure the charcoal is DUST and add some boric acid to help wet it. 

On the topic of metal bits in flux, I like many don't find the idea appealing. But It should be noted that cast iron powder would typically have a lower melting point than steel. I have always suspected that "iron fillings" in good flux that worked was actually cast iron that lowered the melting point at the weld by adding carbon. It also would scavenge excess oxygen. It has been on my radar to play with, just no time for it recently. Seems like a reasonable thing to try with anhydrous borax. 

Ps JHCC, if I didn't mention it before your original posting here on borax has to be one of the absolute best, most accurate and useful posts on all of IFI. 



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Of course a forge weld is NOT a "melted surface weld"  it is a solid phase weld!  Having hot and clean surfaces just makes it easier to get them to "stick".

Of course if it works; it works---even if we don't know exactly why it works!  (Reminds me of a tale of a fellow who in WW II led his lost platoon out of the jungles of Burma using a map----of the London Subway System; he was illiterate...)

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I don't claim to be the guy who thought of using charcoal in flux but as far as I remember or have read I gave it a shot and talked about it here. 

I was inspired to try charcoal after watching a number of different videos of 3rd. word smiths working. Some were anything but 3rd. world but I focused on the most basic kits and materials.

A common theme is the traveling smith arriving at a village and villagers bringing food, scrap and things to be mended or made. The smith I'll reference dug a shallow hole with a trench leading maybe 18" +/-. He bundled a few sticks with pebbles in the center of the bundle and laid it in the bottom of the trench then covered the bundle with stiff mud. His bellows was a bag with a short piece of pipe sticking out of it, he put the end of the pipe against the bundle of sticks and covered it.

After that village kid brought him wood and bid for the privilege of pumping the bellows. Some videos showed bamboo tube and plume bellows, some feather some grass.

While the fire got going, he used a Zippo to light it, he examined the scrap offered in trade and they haggled over prices.

When it got down to it the demand was machetes and brush knives. He used the leaf spring for smaller blades but made the long blades by forge welding fenders and bumpers together. 

While he waited for a "billet" to come to heat constantly coaching the kids at the bellows, mostly slowing the enthusiasm of his thralls he'd chew a piece of charcoal. 

When he brought the "billet" from the fire he's spit charcoal slurry on the joint, pop it back in the fire till it came back to heat then weld it. 

The videos are edited but there was plenty of scenes of the smith spitting charcoal goop on the joints and they rarely failed to get good welds. They charcoal spitters never tried welding without their "flux."

The most prep I saw being done was a quick rub with a handful of sand to take off fuzzy rust, they just burned paint off and rejected plated. Bumpers were desirable stock and chromed ones didn't seem to be common. Axles were often tucked away in the smith's property. One used a nice axle anvil others were just steel blocks some on spikes.

I watched a video by a Japanese sword maker who laid a piece of rice paper between layers he welded.

Anyway, that's what inspired me to give charcoal as a flux or additive a try. I make no claims other than it seems to work and well. 

I leave it to others to decide if it's worth trying. 

I should stop talking flux prices I guess, I haven't looked at one of the online blacksmith suppliers in years. My price data is very dated and probably wrong.  

Frosty The Lucky.


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9 hours ago, anvil said:

I think the old Easy Weld had iron filings in it, while Cherry Weld and Climax don't.

The very old box of Climax that I have does have what looks like iron filings in it. It was given to me by Ike Doss and was opened, so he may have added the iron filings. A very good flux that I save for problem welds, all others get 20 Mule Team borax.

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On 10/8/2021 at 9:25 AM, JHCC said:

The original discussion was here

Thanks, I read the whole thread, And I havent used the big three fluxes in a long time, so I just dont remember which had iron filings added.

I saw nothing in the original post that indicated carbon was worth adding to a home made flux. 

Removing O2 is mentioned and somehow carbon helps. Perhaps it helps by burning it up. Lets look at this a bit closer. When we work our iron, particularly forge welding, we must have a neutral or reducing fire. This means, with 4" of coke under your work and 2" above, O2 is consumed before it reaches your work. Thus and formost, good fire control is needed and this takes practice. Why does a fluxless weld work? Proper fire control is a must, or it will fail. To my way of thinking, proper fire control eliminates O2 from the equation. Does proper fire control consume all of the O2? I dont know. Does a neutral\reducing flame on your torch or in your gas forge have any o2? Im pretty sure that in the envelope the answer is no. I have every reason to believe the same applies to the neutral/reducing envelope in my coal forge.

Next, In a coke fire, our work is surrounded by a literally pure carbon and its in contact with your work. So why add it to your flux, its already there. 

Finally carbon doesnt melt, it burns. When carbon burns it turns to clinker and ash. Seems to me that these two harmful bits of Gradoo are now part of the slurry surrounding your soon to be attempted forge weld. Why add it when you want to get rid of it? Its always good practice, like Turley said in that post, to give your iron a rap, sling it, or wire brush this gradoo off your work before you forge weld. This is a standard practice for me. 

I believe I have given good reasons to not add carbon to your flux. It appears that the reason given in the other post was "I added carbon powder to boric acid and i got a lot of sparks. I lowered the air blast and it appeared to me that it forge welded at a lower temp"(paraphrase). Oh, and it was really runny. A personal observation is a good thing, but should be taken with a grain of,,,,carbon.  ;)

There are 3 reasons to flux.

1:To float away scale and impurities that occur whilst you are bringing your iron to a forge welding heat.

O2 causes scale. When you reach a neutral/reducing environment, this is no longer an issue.

2:It creates a seal around your work. We like to think this prevents scale from forming, and it does,,, as we approach a neutral/reducing enviroment. After we reach a proper fire, scale wont form because there is no O2.

3: It lowers the forge welding temp. This it does, but I don't know why. 


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Wasn't Willow Charcoal used for black powder as it left little ash as compared to some other higher silica woods?  (The use of rice straw ash as a flux by the Japanese sword smiths also comes to mind.)

Gradeau----I haven heard that term since Frank Turley was using it at a demo down here!

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Rice straw ash does indeed contain about 85% silica, much more than wood ash. That makes sense for its use in Japanese bladesmithing.

Regarding the preferability of willow charcoal for black powder, I read a very interesting article about this in Icon (the magazine of the International Committee for the History of Technology). If seems that the choice between different charcoals had to do with the porosity of the wood, since greater porosity means a greater surface area-to-mass ratio and thus faster oxidation of the powder once ignited.

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My intent with adding a carbon source to flux was based on a couple things. 

1. Carbon lowers the melting point of iron (and thus the welding point as well). I can't say a knife maker would care to do that, but to someone welding mild steel it could be very handy. 

2. Carbon bonds with Oxygen, if you are trying to insure that a joint has no free oxygen to make scale then why would you not add it? The tiny little bit of ash in charcoal is likely less of a problem than all the old scale, rust and crud that many of us successfully leave in our welds anyway. 

3. I run propane. Adding carbon to flux in a coke fire would seem pointless to me as well.  Even though I can tune my burner for welding there is a LOT of poorly running propane forges out there. Many shipped new from the factory with terrible tuning. Adding a little insurance for newbies and people not inclined to tune a burner seems like a kind thing to do without causing much of a problem that I can see.   

Even running a well tuned propane forge I was never able to get leaf spring to weld to itself until I tried adding charcoal dust.  

It seems to me that making personal observations is one of the cornerstones of the scientific method. I feel sorry for anyone that feels they need to discount someone else's off hand and without any experimentation, as they are doomed to follow the crowd their whole life.


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20 minutes ago, ThomasPowers said:

I wonder how they worked it out experientially...

I don't think they would have tested the available charcoals for porosity and then selected the one that worked best, but simply observed which ones were better and more reliable in practice. The point of the article was wood preferences for pyrotechnic charcoal were well known and documented since the late medieval period and that their respective degrees of porosity track well with their degrees of preference.  It wouldn't take using very many batches of oak charcoal in gunpowder manufacture to realize that it didn't work as well.

Another reason (at least initially) for a preference for willow is the degree to which it was grown in coppices and thus provided a reliable and consistent source of fuel. It seems that the DuPonts planted a lot of willows in Delaware to provide the charcoal for their gunpowder manufacturing, with women and children often being put to work peeling the branches to hasten drying.


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I would like to point out that the validity of experimental results may have little to do with the validity of explanations of why something worked. We humans are often guilty of "post hoc ergo propter hoc" reasoning as well as other fallacies.

"I did this and it worked" is quite different than "I did this and it worked because of the alignment of the planets or the pH of the water or Dumbo's magic feather..."

Reading a lot of historical documents they were often spot on getting something to work; but if they tried to explain *why* that worked---then things could be pretty off.

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Lol, good thread!  

tlmg, I hope you will notice i commend personal observation. However, and no offense meant(maybe a little tongue in cheek, but only a little  ;) ) A couple of personal observations and assumptions leaves a huge area for error.

Thomas, tlmg used powdered charcoal, and Im talking of coke and charcoal. Both are, for all practical purposes "pure carbon". Of course they are not pure. Both do in fact burn down to ash and clinker. You are talking of another critter completely,,, chemical carbon, or whatever it may be called.   And yes, Gradoo is a Turleyism that i got from him and use it quite a bit because as a descriptive term it is more often than not,,, Right on the money. If you read the OP, you will find a Turley gem and he gives a little history and a different spelling than I use here.  

tlmg, back to adding charcoal to flux and your three points above. I'm trying not to be nitpicky, but hey.

1: I do know some of what carbon does for iron. Basically adding it in a smelting process creates steel. So when you say it lowers the melting point and thus its welding temp, I know this to be true at least for welding, when done in that manner. I also know that adding carbon to iron/steel can be done by the case hardening process. However, this takes a very controlled environment and time. Far more time and a completely different environment than we get when we forge weld. I also know that, contrary to "i saw it on youtube", that you cannot add carbon to steel in a forging environment. So, for these reasons, I cannot accept your point #1.

2: "why would you not add it?" I know that with proper fire management in a coal forge, proper adjustment of a oxy/acetl torch and a gas forge, you should have no O2 in the envelope. My answer is if you do the above, why would you want to.

3: Heres the subjective opinion one. " Adding a little insurance for newbies and people not inclined to tune a burner seems like a kind thing to do without causing much of a problem that I can see:" Personally, I think the kindest thing you can do for these folks is to teach them proper setup, proper job. Teach them proper fire management and proper gas forge setup. And if they refuse,, then why waste your time on them?  Different strokes for different folks, I guess.

I state again, Experience, not flux, makes for the best forge welds. Flux has its place, but will fail without proper setup. 

I'm pretty confident using coal and gas for my blacksmithing. I don't believe i've ever attempted welding two pieces of leaf spring in a gas forge, but I have no doubt I can do it. I have forge welded it in my coal forge. personally, I think you are shorting yourself. Did you ever consider that just maybe, when you popped that weld in your gas forge, you got it because that was the moment when your experience and many attempts finally came to fruition? And you just happened to add carbon to your flux?



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2 hours ago, anvil said:

I don't believe i've ever attempted welding two pieces of leaf spring in a gas forge,

You don't BELIEVE? Don't you KNOW if you've welded leaf spring in a gas forge?

You might want to just let it lay Anvil, you are commenting on something you have no experience with as can be shown by your attempting to compare a properly tended coke fire with a very different set of conditions. 

The conditions created by tuning a propane forge to reliably weld without flux would pump out dangerous levels of Carbon Monoxide in the exhaust.

I'm not about to try and convince you of something your traditional prejudices say isn't true. 

I'm just offering you a little friendly advice and suggesting you stop trying to explain away something you have no experience with. 

Frosty The Lucky.

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18 hours ago, anvil said:

I'm trying not to be nitpicky, but hey.

Lol, we are all nitpicky in one way or another.

I know I may not convince anyone to try out what I am saying, and that is fine by me. I think that sadly they are missing out on something good.

As for item number one you are completely missing the point here. I am not trying to add carbon to the metal, just the weld joint.  No need for special conditions or lots of time as the carbon only needs to react with the first atomic layer in the weld.  Also, just to be clear I didn't quote You Tube, so please don't lump me in with the jumble of idiots out there. 

It honestly may NOT be a good idea for you, especially in a coke forge. But why try and stop anyone else from trying it in a propane forge? The reasons for trying it are sound, even though it doesn't seem beneficial to you. 


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tlmg, " I am not trying to add carbon to the metal". I didnt miss your point. Reread my post, its pretty clear what I'm saying. Basically, I stated what I know what carbon does when added to steel when its being made, and two ways to do this. When you do this, it changes the heat specs due to adding carbon. Its the only way I've ever heard of that carbon has an effect on steel,,, other than you. 

You are making a claim that carbon can change the heat specs of tool steels if you add it to flux, put it on your material and poof it happens. A quote from you above: "the carbon only needs to react with the first atomic layer in the weld". Now you are saying that when you do this, somehow the carbon reacts with the first atomic layer. All I can give that statement is a big,,, Say What??

Again, To be clear, I'm not trying to convince anybody of anything. You have made a statement and I'm trying to get more info from you to back it up. Thats it, nothing more.  

" The reasons for trying it are sound" I have reviewed this thread and the OP where you first brought this up in '16 and have found no sound reasons given. The only reasons given is it appeared to weld at a lower temp and you did a weld you werent able to do before. out of curosity, how many times have you tried this? Oh, and what brand of charcoal did you use?

You bet, With that to go on, I'm beyond skeptical. Theres too many other possible reasons for you to pull off your forgeweld. I'll stick to my above and give you a big congrats on reaching an experience level that made it possible and you just happened to have charcoal dust added to your flux.. 

Frosty, I noticed that in the OP you mentioned you did a fluxless weld in your gas forge. Congrats on that.  

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10 hours ago, anvil said:

Congrats on that.  

This is all just based on my personal experience, which very clearly is much less important than your personal experience. I obviously am not going to convince you of anything so I am done discussing it with you.

To anyone else reading this I urge you to think about what we KNOW carbon does when it is in solution with iron. The melting point gets lowered with increasing carbon. So common sense should make any reasonable person consider that it may have an effect to the faces of a weld joint as well.    


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