I've met him, chatted briefly with him at Ross Farm when the Maritime
Blacksmiths held meets there. I don't know him well enough to know
what his level of expertise is in dating old iron.
You can get a start with a 10 minute tutorial:
Does it look like it has wood grain where it has rusted deeply?
Probably before 1880 and the Bessemer process.
Very rough guess, not reliable. Artifacts can sometime be roughly
dated from their style/design. Nails are interesting: hand-forged
nails, machine-cut nails, modern wire nails. But then you find cut
nails that have have a 3- or 4-clout head hand-forged, presumably for
esthetic reasons, as well as other variations.
I have two axe heads -- both wrought iron with steel bits forge-welded
in -- dug up in my back yard. One is a style made throughout much of
the 19th c.; the other is an 18th c. style of felling axe with a very
interesting detail that a career metalwork conservator might date but
I can't.
I once had a guy in Mahone Bay call and ask me to come and date his
collection of iron objects -- mostly fireplace tools and furniture.
He was initially delighted when I pointed to one item and said that I
could date it very accurately. It was, you see, because I had made it
sometime in the preceding decade. There was a lot more guesswork with
the rest of his collection of 17th-20th c. iron.
--
Mike Spencer Nova Scotia, Canada