Robert, thats a great article and very informative on mobile smithies. I really like your historical setup, its a great way to do experimental archeology that I think is very important to add to academic research. However, I see a few errors in your conclusions Id love to discuss with you.
First off, you assert steel was only made through case hardening. True the Romans used case hardening (mostly in later periods I believe) but not exclusively and certainly not in the method you described. The most efficient way would be to seal many ultra thin bars of iron in a clay box with charcoal and baking them at high welding temperatures for a few hours. These were then welded and folded up a few times to make a relatively homogeneous steel. I would still never call any roman iron or steel "mono-steel" that term is too modern for us to appropriate to this period. The carbon content is still going to vary between layers and the slag/grain would be easily visible especially after some wear and contact with water/anything corrosive.
Ive brought this up on RAT a few times that ancient steel and modern steel are so different in structure we cant really compare them. Have you ever forged iron straight from the bloom? Its very different from a solid mono steel where you know exactly what the content is and there are no impurities to cause crumbling, cracking or weld failures. Even wrought iron from a hundred years ago is a different creature than C45. You have to consider the grain just like in woodworking.
That being said, I have seen a few experiments in case hardening an "accordion" shaped bar before its welded by heating it to welding temps in reducing (carborizing) environments which exist just below the tuyere. After 30 minutes the bar can be welded simultaneously in a few layers that will have increased carbon by a few points of a percent. This was probably known to the Romans but still very different from what you described.
There was also a more common way of refining steel documented by Aristotle that we often forget existed. Hearth refining iron was a easy and cost effective way to make fairly high carbon (.45-.8%) This involved allowing iron bits to descend into a shallow charcoal hearth fed by air from the side and conglomerate under the tuyere into a bloom-like puck.
You also made a rather bold statement that Roman steel never surpassed .45 percent. Why is this? Have the laws of physics changed in the last 2000 years
. Just kidding, but seriously I think its really safe to say the Romans where aware of both how and what techniques would have increased carbon content beyond that point (they probably didnt know it was carbon specifically doing the trick). Whether or not they did was was another question. For example, I assume (based on previous posts you've made) you draw that conclusion from the fact that almost every gladius we have dug up is .45-.50% carbon which would seem on the lower side for blades to modern blacksmiths. If this was the highest they could get, how then did their files scrape the surfaces of the blade? How did their engraving and inlaying chisels cut into them? They had tools that surpassed this amount. I know this for a fact because I have forged and tested Roman steel tools myself (chisels, hammers etc). Since I dont have machines to precisely detect the carbon content I have to use my blacksmithing knowledge to figure it out. A quick spark test shows me the content (on the steel edges backed by softer iron) are well above .45% carbon. My estimates would be .6-.85% in some cases.
Anyway, Id love to discuss Roman blacksmithing and iron making. I really love your traveling smithy setup and I think your assumptions on its functions are well grounded. We should collaborate on a project sometime involving iron and steel made the same way the Romans did.
