AndiTheBarvarian
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Post by AndiTheBarvarian on May 24, 2024 21:48:59 GMT
About the complex pattern welded migration era swords. From forged in fire I learned that the black parts after etching are carbon steel and the bright parts are nickel steel. I assume that in migration era swords the lower carbon parts are the bright ones, or am I simply wrong here? Because I'd then expect black edges on a etched migration era sword and pattern in the middle. But all the repros I see have bright edges.
Edit: Very easy: What is darker after etching, high carbon or low carbon steel?
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eastman
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Post by eastman on May 25, 2024 3:42:47 GMT
they probably polish the edges after etching to make them bright
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Post by mrstabby on May 25, 2024 8:47:43 GMT
Lower carbon steel is more prone to corrosion, therefore it should darken more than the higher carbon content steel. BUT if you get the low carbon steel from a source that has for instnce chromium as an impurity it would likely turn around. I guess it would depend on the source of the steel, how much and what impurities are in it. They surely just grind the edges, since where you etch it won't be sharp anymore (or at lest not as sharp).
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AndiTheBarvarian
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Post by AndiTheBarvarian on May 26, 2024 5:39:05 GMT
After some research: In modern blades for strong pattern contrast you use nickel steel for bright parts and high manganese carbon steel for dark parts. My favorite source for sword technology says this for antique swords: Bright steel. Phosphorus-rich wrought iron might be best Dark steel. Maybe phosphorous-free medium steel - whatever will provide for a good contrast to your bright steel. Hard steel. Needed for the edge. Your steel should have at least the eutectoid composition (0.7 % carbon). Take the highest carbon concentration you can still work with since you will loose some carbon during forging. www.tf.uni-kiel.de/matwis/amat/iss/kap_b/backbone/rb_3_1.htmlI assume the result has less contrast than modern blades show. Makes sense to me.
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Post by mrstabby on May 26, 2024 7:36:00 GMT
Phosphorus rich iron/steel isn't something you want for a blade. Of course that's the easiest way since they did not use ferric chloride but simple acids, those won't pop as much and might need the phosphorus' help, but it also makes iron brittle.
EDIT: Here they say what they used I am not sure the migration era people would have used the same etchants. Result I imagine would depend on the action of the etchant, just removing stuff like pure acids on polished blades or adding layers like theirs does.
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AndiTheBarvarian
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Post by AndiTheBarvarian on May 26, 2024 7:51:06 GMT
It's nothing you'd want in a modern made sword of course. But I 'm interested in the real look of an antique pattern welded blade compared to modern reproductions. Wurmbunt!!!
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Post by mrstabby on May 26, 2024 7:59:43 GMT
It's nothing you'd want in a modern made sword of course. But I 'm interested in the real look of an antique pattern welded blade compared to modern reproductions. Wurmbunt!!! Probably something like this, with the raised sections being the higher corrosion resistance steel.
EDIT: Dark etchants like ferric chloride were discovered in the 14th/15th century, although some sources say "rediscovered" so there could have been a few really darkly etched blades around even then. You could also etch deeply with acid, rust or oil blue and polish the blade, would also leave the low corrosion sesistance/phosphorus rich metal as darker, maybe they did this?
Looks like the chloride etchants stick more to harder steel, interesting
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Post by larason2 on May 26, 2024 14:17:32 GMT
The lines in old school blades are from the silicon and other elements incorporated into the weld lines. This is the same as in wrought iron. You get slight differences in aesthetic between carbon steels of different carbon concentrations, but they're very subtle. So if you want a pattern weld like they did in the migration era, you need lots of folding/welding.
I asked the folks at the blade smith forums about the colour of etchants, and they said there is usually some sort of patination that goes on to give the colour. The patination relies on free iron floating around, so that's why the etching is important. From my other research, etches that look white seem to be related to chlorine being present, maybe some kind of FeCl. Etches that look black or brown one of the varieties of Ferric Oxides. The pH of these etching reactions is very complex, they're redox reactions that require a particular pH, but it's not as easy as acid creates one patina, base creates another. I think that when Hato stones are used in sword polishing, patination is part of the effect, but they are a very mild acid, only pH 6.8 in my measurements. More likely it is a complex redox reaction.
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Post by mrstabby on May 26, 2024 15:59:22 GMT
Beyond pH4 acids don't patinate, they just dissolve iron. It's probably not that complex, likely just stealing an electron or two from surface iron making it soluable. I think the dark appearence is just the surface being rough (at least on mine it looks like it, hadn't thought of looking through a microscope), iron oxides would not survive under these conditions any better than the steel. The ones with a more soft difference just look like hills and valley, the ferric chloride seems to pit more and more selectively than other acids.
EDIT: I think I made a mistake. So yes mild steel is less corrosion resistand than high carbon, but only at the same hardness! The harder steel is a more energetic state and therefore it's easier to dissolve surface atoms from there. So the phosphor iron remaining bright vs the carbon steel darkening makes more sense. There is no deposition of material, it's only a physical difference in surface finish. Unless you use coffee or something that really does produce different surface oxides. That also explains why my softer blades won't rust as easily as the harder ones, no matter what they are made of.
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Post by larason2 on May 26, 2024 18:27:08 GMT
I don't think the dark appearance is the surface being rough, because that means as you polish it should get lighter, but that's not always the case. In the case of the traditional Japanese brown patination, the patination reaction won't happen unless you have sulfur and copper II sulfate, Iron bearing clay, potassium nitrate, and ferrous oxide powder. When you apply it and heat it, you get the strong smell of sulfur gas. Clearly the sulfur is an electron donor, by why does it need copper II sulfate if it has elemental sulfur or vice versa? Also, why does it specifically need the clay? Ferric Chloride is a simple solution, but the patination is a bit more complex. You just need to look at the wikipedia article, which states in water it's an oxidizing agent, and anhydrous it's a lewis acid. en.m.wikipedia.org/wiki/Iron(III)_chlorideYou need a strong acid to dissolve ferric Chloride in water, but that doesn't mean that the resulting solution is unable to react with iron. Perhaps it removes metal, but I'm pretty sure that's not all that's going on.
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Post by mrstabby on May 26, 2024 18:50:26 GMT
I don't think the dark appearance is the surface being rough, because that means as you polish it should get lighter, but that's not always the case. In the case of the traditional Japanese brown patination, the patination reaction won't happen unless you have sulfur and copper II sulfate, Iron bearing clay, potassium nitrate, and ferrous oxide powder. When you apply it and heat it, you get the strong smell of sulfur gas. Clearly the sulfur is an electron donor, by why does it need copper II sulfate if it has elemental sulfur or vice versa? Also, why does it specifically need the clay? Ferric Chloride is a simple solution, but the patination is a bit more complex. You just need to look at the wikipedia article, which states in water it's an oxidizing agent, and anhydrous it's a lewis acid. en.m.wikipedia.org/wiki/Iron(III)_chlorideYou need a strong acid to dissolve ferric Chloride in water, but that doesn't mean that the resulting solution is unable to react with iron. Perhaps it removes metal, but I'm pretty sure that's not all that's going on. There might be some oxidation going on but that's not the ferric chloride alone. 2 FeCl 3 + Fe → 3 FeCl is what happens with ferric chloride and FeCl is a very stable result which would not do much without a kick from something else, of course it a bit of it could stay back colouring the holes, would explain the green tint. I hope on the picture you can see how deep these etching holes are, they would not polish out, you'd need to grind a bit. Just guesstimating it's a few dozen µm deep at the shallowest.
The patination likely lays down a layer of elemental copper, not unlike Oberhoffer's Etchant from the TU Kiel, this is why it only works with copper sulfate and sulfur. I am not sure where you got that ferric chloride would be insoluable in water, it dissolves easily in water, most chlorides are.
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Post by larason2 on May 26, 2024 19:00:17 GMT
Maybe the only places you'd get the FeCl with the attached iron in the right position to coordinate the reaction are deep in the holes? Anyway, that picture doesn't look like it just has holes to me, they look blacker than you would expect. Plus, we know other acids like HCl don't etch steel the same way that Fe Cl does, but they should also dissolve away steel, so what explains the difference?
I could be in error about the Fe Cl solubility, but I know it has a low pH.
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Post by mrstabby on May 26, 2024 19:14:45 GMT
Not all acids do the same, they have preferences, like HCl and H2SO4. Yes both eat metal and organics, but one does metal faster the other organics, by a lot. I think the Fe(3)Cl is just in the right place to not dissolve everything at a more similar rate as HCl would. I think the colour is Fe(2)Cl which would result after a reaction of iron and the Fe(3)Cl. It is the right greenish colour and the holes likely also protect it from getting washed away. It could be some Fe(2)O2, but this would not be stable at a lower pH or it would arrest the reaction, so the only time it could form would be at higher pH, while washing off the solution or with a bath afterwards. Of course where there is one Fe2+ species there could be others, but it would need a lot of oxygen as well.
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AndiTheBarvarian
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Post by AndiTheBarvarian on May 26, 2024 19:55:06 GMT
From King Theoderic's "Thank You-Letter" to King Thrasamond:
These swords are richer for their iron than for the value of the gold [which embellishes them]: for there flashes out from them such a polished brilliance that they reflect with the utmost fidelity the faces of those who look at them. Their sides approach the edges with such uniformity that you would think that they were not fashioned by files, but cast from fiery furnaces; their centers, hollowed out with beautiful grooves, seem to undulate with worm-like markings; for shadows of such variety you would think the metal was interwoven rather than shining [superficially] with different colors. The metal your whetstone so carefully shapes, this your splendid dust (granted to your country by the bounty of nature) so thoroughly polishes that it makes the gleam of the iron a very mirror of men.
I assume those blades were rather polished than etched but still had a visible pattern in the fullers. But also not just black/bright.
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Post by mrstabby on May 26, 2024 20:07:05 GMT
The core would have been wrought iron, right? This would have innate beautiful patterns from inclusions. I am not sure if polishing alone does it or if you would have to do something else. It would likely be either highly polished or a tiny bit etched but AFIAK the inclusions of ferrite/slag could have enough contrast with polish alone. www.vikingsword.com/ethsword/pat01.html
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AndiTheBarvarian
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Post by AndiTheBarvarian on May 26, 2024 20:13:23 GMT
The core probably was made of twisted bars of wrought iron and steel. Maybe the polishing "dust" contained some acid Iike the Japanese polishing stones. The result seems to have been a mirror polish but with a visible worm pattern in the middle.
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Post by mrstabby on May 26, 2024 20:26:33 GMT
I mean it could be just like the difference between stainless steel and carbon steel where one is more grey and the other more silvery when polished, but I have never really used wrought iron or polished it, also modern wrought does not have that same pattern as the ancient.
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Post by larason2 on May 26, 2024 21:33:23 GMT
There's a spectrum of burnished polishes, some of them you can see zero metal detail, but if you do it just right, you can see some metal detail. That's the purpose behind the burnishing the Japanese do on the shinogi of a sword. First they carefully polish it with an open grain/textured sort of polish, then carefully burnish it. It's burnished like a mirror, but you can still see the details under to some extent (primarily welding lines). That's probably what they're talking about in King Theodoric's letter. I'm guessing this was almost certainly done with stones, since this is what they had in 471, but they could have done partially stones (or stone powder) and partially with a burnishing knife. Polishing with stones is never just one thing, depending on technique and the grit you can get pure open grain abrasion, but with the right stone you can also just burnish it so no detail is left. From my research, it seems that there was a variety of practices, from the beginning of sword finishing. For instance, we know some bronze swords were "white bronze," whereas others were more "gold bronze." From my experiments with 11% tin bronze single cast, if you burnish it it comes out white or silver looking from the right angles, if the polish is open grain, it looks gold. So they probably were using both or a combination well before there were even steel swords.
It's true different wroughts have different appearance, but that all comes from what is used as the flux when welding. Modern smiths almost exclusively use borax when welding, which probably gives the most vanilla appearance (but can still give some nice welding lines). In Japan they use ash from the burning of grass/reeds, and that tends to give a very nice multicoloured/faceted sort of look if polished correctly. Smiths here try to use grass ashes as flux, which works, and is nicer than borax, but they don't quite get the same effect. Still, if you get a pattern welded sword where they used ash or something like that as the flux to weld it, it has the potential to be every bit as nice as the blades they had at the time of the goths. Such a blade is very pricey though! Ash is harder to use as flux though, and not all grasses and other ashes work as well as others.
As far as I understand, just like in Roman times there was a variety of different irons used to make swords. Some were pure wrought iron, which doesn't harden, and so, doesn't really ever hold an edge well. If you have a rock handy though, you can just keep sharpening it whenever it needs it. I believe in some places they already knew about case hardening though, of some form anyway, and so some wrought iron swords were case hardened one way or another, though the quality of this hardening was sometimes a bit sketch. At the other end of the spectrum though, there were some smiths that were making proper carbon steel from the bloomery technique. However, there was also a range of this, as carbon output in the steel can vary a lot depending on the bloomery design and technique. The best smiths though knew they were making proper carbon steel, and used that for the edges, whereas the core was generally more standard wrought iron, or something with less carbon made through the bloomery technique (the higher the carbon content, the harder it is to forge, I know this from experience!). So you'd have to look at the composition of the actual sword to say what it was made of or how good it was, there was still a range of different qualities in the examples we have found.
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