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The Absolute Last Final Word on Anhydrous Borax Flux


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Hello from northern Wisconsin.  JHCC, thanks for the thorough write-up.

A few decades ago I spent a week throwing sledge for a guy who was getting into forging tomahawks.  We fluxed with straight boric acid, and although I recall it working well, neither of us had enough experience to know otherwise.  Fast forward thirty-five years and my sons are messing around with a gas forge.  They're coming along, and I'm sure welding isn't far down the road.

I've spent a bit of time using the site search function and have read this very thorough thread, but haven't found any posts addressing straight boric acid as flux.  Looks like it is chemically very similar to borax, less the sodium atoms (and accompanying high-temp sodium flare).  Does anyone have experience to compare straight boric acid to anything else? 

Here to help, like to learn.

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Yeah, I get that.  We're set up on the cheap here too.  But I'm seeing 10 pounds for $25 or 5 pounds for $18 on Amazon.  That'll keep casuals like us running a long time.  Do ya know if it works any better or worse than anything else?  I just don't want 10 pounds of regret.

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I've never used just boric acid, I mixed my own borax, boric acid flux before I bought a can of Peterson's #1 blue at the welding supply. 

Boric acid has a lower melting temp than borax so it'll provide a prophylactic barrier against contact with atmospheric oxygen. Doing it at a lower temp means less scale can form before the barrier forms.

I was looking through the fluxes at the local welding supply for giggles one day while waiting my turn. Reading the ingredients on commercial: welding, brazing, hard soldering, etc. fluxes listed what I was seeing in the high dollar "forge" welding fluxes being sold on blacksmith sites. No one listed the borax content as "anhydrous" so I asked the guy at the counter and they said come on back. I went into the backroom and they had open containers of every brand and type they sold and handed me a torch and pointed at the scrap and welding, brazing, etc. rods. 

It was just like using the granular brazing flux we used in jr. high metal shop, warm the rod up, dip it in the powder and weld, braze, etc. with the now flux coated rod. 

A 1lb. can of Peterson's #1 Blue was $26 on the shelf in Wasilla Ak. shipping included. A 1lb. can of one of the commercial forge welding fluxes on a blacksmith supply site was well over $100 plus shipping and listed the same ingredients. If you want  powdered iron in your forge welding flux that's Peterson's in the yellow can I THINK, read the ingredients, they're on the label.

I've used and shared that can of flux for I don't know how many years and it's down maybe 3/4 cup and will undoubtedly be available at my estate sale. 

Frosty The Lucky.

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I’m not an experienced master smith or even an apprentice for that matter lol,

    I just started on learning forge welding and I used the Peterson’s no1 blue flux an all three of my first welds stuck on the first try,

I got mine online for $20 something an free shipping, i still got a long way to go learning but I’d suggest it to anyone else in my position starting in on forge welding

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A number of fluxes (Iron Mountain, for example) contain metal particles. As Latticino explained to me once, it’s a little extra insurance, just like having a bit of boric acid to lower the melting temperature or some finely powdered charcoal to scavenge oxygen from inside the weld. 

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12 hours ago, Jack Rotts said:

Frosty, you mentioned in a 2017 post using Peterson #2.

I misspoke, I use #1 blue. No metal dust for me thank you. I know a lot of people swear by it but so many contain iron OXIDE powder and I've never understood why anybody would introduce iron oxide into a weld when we do so much prep work to eliminate the oxides.

Frosty The Lucky.

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If there really is a genuine reason, I suppose it might have something to do with the specific iron oxide. Adding Fe₃O₄ would make no sense, because that's the same oxide as the scale that forms in the fire. Adding Fe₂O₃ (rust) might have some beneficial effect with scavenging oxygen or reducing melting temperatures or something, but I'd want to see the actual chemistry on that before I'd include it in my own flux.

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I'm reaching back many years into the memory banks but I seem to remember that iron/steel dust or small fragments, e.g. filings, were added to some commercial flux formulations or home made flux recipes.  IIRC, the purpose of them was to spark before the workpiece and give a visual sign that welding temperature had been reached, not to add anything to the function of the flux in excluding oxygen from the weld area.

This is a somewhat vague memory and I may not have it correct but the theory makes some sense to me.

"By hammer and hand all arts do stand."

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Iron filings and you could see little pimples on the outsides of welds when they were used.  I don't know if they were sacrificial temperature indicators or were expected to heat to welding temp faster to aid getting the surfaces to stick.  For billet welding you don't want anything in the weld zone; so I don't have a lot of experience with them.

IIRC Patrick did some flux experiments when he was studying metallurgy way back when.  I wonder if he tried filings, and or scale; I know he tried adding carbon to a flux.

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I've added powered charcoal to Peterson's and it seemed to make it stickier welding. My thoughts were, the carbon scavenged oxygen preventing scale or perhaps reducing it and secondly it increased the carbon content at the joint reducing the melting/welding temp.

Am I right?  I don't know but it makes Peterson's weld a little easier or so it seems.

Frosty The Lucky.

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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.

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I’ve heard that adding iron filings to flux help to keep your scrafs from slipping during the initial setting of the weld. Kind of like putting barbs on an axe bit. Not sure if there is much truth to it though. The last batch of flux I mixed up I added some and it worked pretty good, but my welds are still hit and miss either way…

David

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I think the old Easy Weld had iron filings in it, while Cherry Weld and Climax don't. I know they have changed their time tested formulas due to EPA or whatever reasons and I have not tried them. 

I did a price check at Centaur forge and think there was a typo in the post above. 5# of forge borax, Easy Weld,Climax, and Cherry Weld is ~$80. one pound of easy weld,Cherry weld, climax, Petersons #1  and forge borax are ~$18. Petersons was a buck higher,,, no biggie there.

I've used all the above, except for Peterson's #1, along with 20 mule team borax straight and with boric acid added. This is the first I've ever heard of adding charcoal. My initial reaction to charcoal is,,, found it on the internet, you say? No judgement, just my initial reaction til there is more information.

I think what makes the best, cleanest, quickest forge weld is practice. 

A lot of smiths go thru a "I dont need no steenking flux" phase. It's kinda like the mile high club for blacksmiths,,,  ;) I know I did. I think most go back to using flux of one sort or another. For those who knew Judd Nelson, He used 20 mule team and would grab a small handful and sorta toss it at his fire,,, never missed a weld even in broad daylight. 

My go to is plane ole 20 mule team plus a little boric acid. If I dont have any boric acid,,, oh well.

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