Historial finishes for pattern welded blades

[Caleb Budd]

Hello all

 

I’ve recently gone down a rabbit hole of pattern welding etching/“revealing” methods available to early medieval smiths (curtesy of the wonderful page member Andrew Welton). In particular this specific quote 

 

“When the Goths had gathered together on a certain day for their assembly, the iron sections and the blades of the spears which they carried in their hands had for a time not kept their natural appearance of iron but changed colour: some were green, some red, others yellow or black”

 

As such I was wondering if anyone has had experience with or has more articles on some more “classical” methods of pattern revealing such as heat bluing. 
 

Thank you’ll in advance! 

[Carlos Lara]

That's interesting. I'd like to read what you've read by Andrew Welton. I saw his page on Exarc. I'm guessing if the blade was green, it was either from copper, or phosphorous crystals. The red and black are probably iron. Not sure where the yellow would come from! Maybe sulfur or iron silicates (from clay). The colours were probably from oxidation of the steel, and were probably unintended, maybe impurities in the metal. However, the surface treatment does really affect how patinas develop, and I suspect that the Celts/Goths used stones/finger stones to sharpen and polish their blades, or maybe stone or clay powder like the Japanese polish urushi. Those stones when used affect the metal's surface composition, and how they were polished affect how crystals can form on the surface. Probably there were small amounts of the stones impregnated on the metal, which affected the patina. They probably also still had some bronze swords, to complicate the picture! For sure they could have treated with chemical patinas, though they probably wouldn't have been surprised later on, as an intentional patina probably wouldn't change unintentionally. A very interesting discussion though. I'm curious as to what the other members will say.

[Alan Longmire]

Without going to the source material, I suspect that quote refers to a temporary paint or dye.  We suspect they only etched very weakly, sometimes such that you can only see the pattern under certain circumstances, ie the famous thing from some saga about a borrowed sword used for a duel that, when gently breathed upon, revealed a serpent seeming to climb the blade from the lower guard.  This is an excellent example of what to expect if breathing hot humid air on a cold, pattern-welded but unetched, blade.

[Andrew W]

That quote where the spears change color is fascinating little passage. It’s from Hydatius, a fifth-century Galician chronicler, and it is describing a miracle / portent, so the details could be intended to sound fantastical—it might be naive to take it too seriously. I mentioned it in that chapter of my dissertation, though, because it reminded me so much of the colors you get from tempering. Could the miracle be that the color changed on its own, and are colored spearheads really such a far-fetched idea when oxide finishes like russetting, bluing, or oil-blackening show up in other times and places?

 

Surfaces on Late Antique blades so rarely survive, and when they do they’ve often been changed during conservation (the spearheads from Lyminge come to mind—some have beautiful polished black surfaces; the polish is original, but the color came from chemical stabilization in the 1950s). Some of the Late Antique spearheads from the Thames have original surfaces, and these are russeted; but they spent 1500 years in anaerobic mud, so their patina today tells us little about their original color.

 

I think the best clue that some of these spears were blued/blackened is the use of silver inlay decorations on several Late Antique UK spearheads. This inlay would have been very subtle on a mirror-polished blade; but it would’ve looked striking if the blade had dark oxide finish.

 

That’s not the only possibility, however. Researchers scanned the spearheads from Mucking with XRF, and found traces of copper plating on their surfaces. And I like Carlos’s suggestion that they might have used paint. Late Antique spearheads so rarely had complex pattern-welding that I don’t know how common the fine mirror polishes would be (where patterns can be concealed until you look closely, as Alan describes) that swords and seaxes of the period seem to have often had.

 

I think we should play with the possibilities. It’s very easy to project the familiar, polished surfaces of early modern spearheads back onto the spearheads of Late Antiquity. And while that’s probably correct—if our historical and archaeological sources give us other options, why not see how those could look, how they hold up, and whether they can teach us anything new?

Edited April 12 by Andrew W

[Dan Hertzson]

Here's a thought:  what if the reference is a bit of poetic license and a description of the timing for the certain day the Goth's gathered (in a transitional forest in the fall for instance).  The colors are the reflection of the forest in polished steel.  Just throwing it out there. 

[Caleb Budd]

Andrew summed up all that beautifully and better than I ever could! 
 

3 hours ago, Dan Hertzson said:

Here's a thought:  what if the reference is a bit of poetic license and a description of the timing for the certain day the Goth's gathered (in a transitional forest in the fall for instance).  The colors are the reflection of the forest in polished steel.  Just throwing it out there. 

possibly! I am in no means an expert in the topic and was looking to gather more information before I start my own experiments on the matter! 

[Aiden CC]

Also worth noting is that a polishing with fine, friable, abrasives avoids burnishing and leaves a more "open" surface, which shows features in the steel better. Stefan Mäder had several early medieval blades polished by a professional Japanese sword polisher with interesting results, presented in "Stähle, Steine und Schlangen". It's speculative, but below is an image from that work showing what pattern welding looks like with a very fine polish with natural stones. 

 

Edited April 13 by Aiden CC

[Caleb Budd]

2 hours ago, Aiden CC said:

Also worth noting is that a polishing with fine, friable, abrasives avoids burnishing and leaves a more "open" surface, which shows features in the steel better. Stefan Mäder had several early medieval blades polished by a professional Japanese sword polisher with interesting results, presented in "Stähle, Steine und Schlangen". It's speculative, but below is an image from that work showing what pattern welding looks like with a very fine polish with natural stones. 

 

I have read parts of that and it’s peaked my interest as well! My only confusion (which admittedly might be silly) is that I don’t understand the difference between that polishing and say using belts. Is it purely just the stones themselves that are doing that or is it the grit?

[Jeroen Zuiderwijk]

I've seen evidence of deep etching on pre-Roman) iron age swords. If you look at some La Tene swords, you see that they did differentially etch the blades. There's a clear step between the un-etched smooth edges, and the deep etched centers of the blades, indicating they protected the edges during the etch, while the center was etched deep enough to leave a step and reveal the pattern of the wrought iron. Although, it is possible that the step was carved in the blade before etching. I don't have a photo to show it at hand, but if I remember I'll add one when I get home. 

[Caleb Budd]

5 minutes ago, Jeroen Zuiderwijk said:

I've seen evidence of deep etching on pre-Roman) iron age swords. If you look at some La Tene swords, you see that they did differentially etch the blades. There's a clear step between the un-etched smooth edges, and the deep etched centers of the blades, indicating they protected the edges during the etch, while the center was etched deep enough to leave a step and reveal the pattern of the wrought iron. Although, it is possible that the step was carved in the blade before etching. I don't have a photo to show it at hand, but if I remember I'll add one when I get home. 

Is there evidence of the same in later pieces circa 6-9th century? From what I remember they weren’t etched so deeply (though I can be misremembering I haven’t brushed up on my books recently). But I’d love to see that picture because that’s super interesting! I’d have to assume they used some sort of vinegar for deep etching?

[Aiden CC]

On 4/13/2023 at 12:44 AM, Caleb Budd said:

I have read parts of that and it’s peaked my interest as well! My only confusion (which admittedly might be silly) is that I don’t understand the difference between that polishing and say using belts. Is it purely just the stones themselves that are doing that or is it the grit?

I think it comes down to the difference between abrasives of different hardness/shapes and how a loose abrasive acts differently than one bonded to a surface. Softer abrasives have a notably different effect on the hardened and un-hardened parts of the surface. They also break down and constantly expose fresh grit so that they are cutting as opposed to burnishing. In addition, loose abrasives cut differently, and the slurry formed on top of the stones also participates in the process.

[Caleb Budd]

3 hours ago, Aiden CC said:

I think it comes down to the difference between abrasives of different hardness/shapes and how a loose abrasive acts differently than one bonded to a surface. Softer abrasives have a notably different effect on the hardened and un-hardened parts of the surface. They also break down and constantly expose fresh grit so that they are cutting as opposed to burnishing. In addition, loose abrasives cut differently, and the slurry formed on top of the stones also participates in the process.

And that makes total sense! Especially when considering the differing hardness you can find in one piece. Thank you very much for that Aiden! After reading what you said I’ve been looking at some Belgian stones that I’m kinda interested in trying out for some blade polishing if it even makes a difference. But I have to assume a big part of the contrast was the differing hardness and metal makeup which would be wildly different than the more modern steel on steel composition of pattern welding.

[Aiden CC]

16 hours ago, Caleb Budd said:

And that makes total sense! Especially when considering the differing hardness you can find in one piece. Thank you very much for that Aiden! After reading what you said I’ve been looking at some Belgian stones that I’m kinda interested in trying out for some blade polishing if it even makes a difference. But I have to assume a big part of the contrast was the differing hardness and metal makeup which would be wildly different than the more modern steel on steel composition of pattern welding.

Composition definitely, though not necessarily hardness difference. A combination of iron/steel and high P iron will behave differently than two steels with Mn, the bright one also having Ni as used in modern steels. I’m not as sure about the hardness difference. It’s not uncommon for micro hardness measurements to be made in sword blade sections but I don’t know if I’ve seen one examining pattern welding. The second material after has some carbon in it, sometime an even being a medium carbon steel, and in those instances may be harder than the high P iron. 
 

The most common explanation I’ve seen in the literature is that the phosphoric iron provides a “light etching” region, while the steel provides a “dark etching” region. This is true when polished an etched for metallography but only because the high P regions become frosted and appear lighter than the still mirror-like regions which aren’t etched as aggressively. When you do a ferric chloride cosmetic etch, the high P regions become much darker. Here is a bar where I tested this out:

 

You can actually see the contrast reasonable well straight off a 220 grit belt in the second picture. This is a very high P iron though, though later pattern welding did sometimes use iron with quite a bit of phosphorus.

[Jaro Petrina]

This explains some weird effect I had etching.