Thanks for your comment, Shelby.
It may be steel, not pure iron. But how could I distinguish steel and iron without a metallurgical analysis?
In the modern world, if my info is correct, 1010 is steel 1008 is iron. Undetectable difference without modern equipment.
Now low quality “iron” would not likely withstand being formed into a flask. It would fail along one the lines of impurities. Because iron from even most of the 19th c. has a LOT of ”$#@*” in it unless well refined. If we work with some iron of the Civil War era we will find many inclusions. Even in things like percussion Sharps receivers which one would think were really good stuff. Nope, until the 1878 model, at least, the CV rifles/carbines and others made from the CW era forgings were riddled with slag and such. I we look to factory guns fo the 1860s, 70s, 80s we find receivers with “forging lines”. I have seen these actually form “fins” when run through a cyanide case hardening process and quenched.
Back in the day they could not easily tell low carbon steel from the better grades of iron. The Rifle Muskets of our Civil War had “best iron” barrels, it was more reliable that steel of the time for this use. Steel or “best” Iron from 1770 is far different in quality than steel or “best“ iron made in 1860. I have had piece of old shafting from a friends scrap pile I was making into a front sight actually fail at an inclusion as I filed it to shape. Piece broke off along a straight line. And I have seen inclusion lines in late 19th c suppository type rifle barrels too.
I believe the better English guns for example were made with “damascus” steel because it was far more refined. W. Green tells us in the 1830s that very good “damascus” barrel steel was made from horse shoe nail stubs. They were melted, formed into a bloom and hammered into bars. The process burned off/removed most if not all the impurities and carbon that would have been in the nail stubs.
Too much info sorry. Got carried away. Not a metallurgist. But I suspect that Mr Kelly post it would be similar but more technical.
So when the flask was made of what ever metal it is, telling iron from steel at least in modern parlance, may have been simply that steel would harden and iron would not.