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Historical Flux


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What was used historically for flux, specifically around the turn of the 10th century and in or around the British Isles? Did they even use flux like in the recent Hot Forge topic?

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Yep, none, or sand, or sometimes salt. Remember they were working with bloomery-derived material, which always contains a little slag and is thus self-fluxing. No alloying elements to screw up the scale either.

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Salt?!? I learn something new every day. Just some facts are more bizarre than others.

 

I suppose salt for flux isn't the most bizarre thing I've heard in the last 24 hours but that is only when considering the Emergency Room kept me up all night doing psych evals for people the cops picked up due to "altered mental status".

James

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  • 2 weeks later...

Yep, none, or sand, or sometimes salt. Remember they were working with bloomery-derived material, which always contains a little slag and is thus self-fluxing. No alloying elements to screw up the scale either.

While doing some practice forging I thought about this and went ahead and tried salt flux even though I wasn't welding, and it seems to work just like if not very close to what I have seen borax behave.

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i tried forge welding with salt once.

the biggest problem with using salt as a flux is that it will rust every iron thing in your shop :angry:

also i think that borax works better,so i never use salt anymore

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The 1860s U.S. Army Ordnance Manuals contain more than one formula for flux for the use of Army blacksmiths.

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I didn't say you should use salt, I just said it sometimes was in the past. ;)

 

It is nasty for the shop air and your lungs, particularly if there's any silica involved such as clay, sand, or (gasp!) smelting slag. When any kind of silica is exposed to sodium chloride at very high temperatures the sodium will bond with the silicon and release the chlorine which, being active stuff, will then usually bond with hydrogen and oxygen to form hydrochloric acid vapor. Incidentally, this is the reaction that causes salt glaze on pottery. Clay has a lot of silica, and when you throw salt into a stoneware kiln at 2200 degrees F (like a welding forge!) it vaporizes and that reaction above forms a skin of sodium silicate glass on all exposed clay surfaces. The chlorine scavenges hydrogen and oxygen and exits the chimney as a thick greenish-white cloud of gas that will be either poisonous (not enough hydrogen to scavenge results in chlorine gas), acidic, or both to some degree or other.

 

I have also tried mud dauber nests since I have seen them mentioned in old books. For those who are not familiar with this creature, it is a type of solitary wasp that builds tubular structures out of clay, usually under the eaves of buildings. They are very particular about their clay, and as such it will always be a good high-silica type capable of being fired almost to stoneware temperatures before melting or fusing into glass. It works on wrought iron, not as good on steel.

 

The reason we use borax today is because it is such a good oxygen scavenger with low toxicity compared to the historical fluxes.

 

Finally, remember that (for western Europe and the Americas) prior to the widespread use of crucible steel in the early 19th century all steel was derived from good old slaggy wrought iron in one way or another, and as such didn't need added flux nearly as much as modern clean steel. That's why there is a sudden explosion of patented fluxes beginning just before the American Civil War (1861-65); the Bessemer process had just been introduced and suddenly steel was cheaper to make than wrought iron, for the first time in history. Clean low carbon (mild) steel took the place of wrought iron, and a lot of blacksmiths had a hard time adapting.

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I didn't say you should use salt, I just said it sometimes was in the past. ;)

 

It is nasty for the shop air and your lungs, particularly if there's any silica involved such as clay, sand, or (gasp!) smelting slag. When any kind of silica is exposed to sodium chloride at very high temperatures the sodium will bond with the silicon and release the chlorine which, being active stuff, will then usually bond with hydrogen and oxygen to form hydrochloric acid vapor. Incidentally, this is the reaction that causes salt glaze on pottery. Clay has a lot of silica, and when you throw salt into a stoneware kiln at 2200 degrees F (like a welding forge!) it vaporizes and that reaction above forms a skin of sodium silicate glass on all exposed clay surfaces. The chlorine scavenges hydrogen and oxygen and exits the chimney as a thick greenish-white cloud of gas that will be either poisonous (not enough hydrogen to scavenge results in chlorine gas), acidic, or both to some degree or other.

 

I have also tried mud dauber nests since I have seen them mentioned in old books. For those who are not familiar with this creature, it is a type of solitary wasp that builds tubular structures out of clay, usually under the eaves of buildings. They are very particular about their clay, and as such it will always be a good high-silica type capable of being fired almost to stoneware temperatures before melting or fusing into glass. It works on wrought iron, not as good on steel.

 

The reason we use borax today is because it is such a good oxygen scavenger with low toxicity compared to the historical fluxes.

 

Finally, remember that (for western Europe and the Americas) prior to the widespread use of crucible steel in the early 19th century all steel was derived from good old slaggy wrought iron in one way or another, and as such didn't need added flux nearly as much as modern clean steel. That's why there is a sudden explosion of patented fluxes beginning just before the American Civil War (1861-65); the Bessemer process had just been introduced and suddenly steel was cheaper to make than wrought iron, for the first time in history. Clean low carbon (mild) steel took the place of wrought iron, and a lot of blacksmiths had a hard time adapting.

Well, now I am glad I only tried it once ;)

Thanks for the heads up!

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Well, just from observation, without thinking through any of the chemistry--- i've used a salt/sand mix some, and it seemed like the point of the salt was that it melted at a low temp and helped the sand to stick 'til everything got hot enough for the sand to melt (or rather fuse with the iron oxide). If you use sand alone, you can't toss it on 'til the metal is mighty hot,

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As a related point of trivia;

I was attempting a while back to refine some 2% C cast iron into steel the same way guys that know what they are doing refine bloomery iron. By soaking at welding temp with borax and then hammer, fold, repeat.

Turns out, borax used as a flux on high silica cast iron, bonds with the silica and forms Borosilcate glass (Pyrex).

The theory did work, in so far as the cast iron welded to the shim stock I stacked it on and after a fold or 2 it stopped crumbling...

 

BUT... When you the strike the bloomin stuff it sprays molten glass like a fountain and totally destroys the front of your pants...

 

That is when my wife bought me a leather apron, and talked me into shelving that particular project.

James

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Ironically the old smith that taught me to weld years ago used half borax/half silica sand for his flux (which he carried in a Prince Albert can in the pocket of his shirt). It was years down the road before I realized that you didn't need the coat of "glass" over the edges of a weld. :)

 

Gary

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  • 2 months later...

How about Pine Rosin?

I know this is probably a dumb question, but I have heard of people using Pine Rosin as a soldering Flux. Does anyone know if that would work for bladesmithing? Or would it just burn up? If so would there be a way to process it so it could be used as a bladesmithing flux?

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I'm afraid pine rosin just doesn't survive at forge-welding temperatures. It works for soft solder because the temperatures involved are so low. We're talking about 450 degrees F max for soft soldering, and 2100 degrees F for forge welding. That's why the various welding fluxes do not burn, they melt into a glass that both absorbs oxides and protects against further oxidation. I can't see any way for pine rosin to be made to work in that application.

 

Borax is cheap and readily available unless you're in the UK where it is banned as a washing additive and you have to get it from a pottery supply. The only reason to use anything else would be for historical purposes, in which case the purest silica sand you can find is your substance. Of course, if you're going that historical you had better be using wrought iron anyway, which with its self-fluxing properties from the incorporated slag the sand just adds a little extra.

 

Modern clean steels need a better flux or a strongly reducing atmosphere.

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For the past couple months I have been learning to use my charcoal forge with all my bloom processing. I have been using nothing but fine pool filter sand as a flux, even in the late stages of many fold bars.
It has worked very well.

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That is faceting! I wonder what the pool filter sand is made from!

 

I have been trying to research methods of smithing that would be least dependent on "store bought" products. I would like to know how to utilize the natural elements in case I ever found myself in a situation where I no longer have the option of going to the store and buying Flux or whatnot!

As has been stated on this discussion, silica can be used as a flux, but what IS silica? I have read that it is processed from Quartz, so is silica pretty much just finely grounded up Quartz? (SiO2=Quartz)

=)

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Yup, it's just sand.

Like Lee said above, when using the just sand, the iron needs to be hot. I have been just tossing a bit on top of the billet, then adding charcoal over that.
I have welded up a half dozen sword billets from bloom this way lately.
I have been pulling out some wonderful PCB's when I clean out the forge. Right out of the archeological texts.

 

 

 

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