Interesting note on the horseshoes etc. used in forging these blades. I am the first to admit my limited understanding of metallurgy, but I find the perspective of finding folklore from observing normal practical functionality quite common during those times. Consider the very superstitious and wary manner which blacksmiths were perceived, and of course the intriguing stories that were often contrived about them.
If the blacksmith was observed adding old horseshoes into the crucible in making steel for blades, of course it is quite possible such deliberate use might be interpreted by superstitious observers for special or even occult purpose. However, I somehow get the impression the author (and I have a vague idea of who it might be
may have deviously meant the comment 'tongue in cheek' with reference to the plethora of folklore concerning arms and armor during these times.
In addition to what Jeff has already added concerning horsehoes and nails being used in making steel, I found the following, which may be the reference Jens had noted,
"...in the Persian method of casting Damascus steel small segments of hammered and polished soft iron or wrought iron, or small hammered and polished pieces of iron salvaged from worn horseshoes and nails were placed in a crucible with carboniferous materials".
"On Damascus Steel", Dr.L.Figiel, 1991, p.18.
I would imagine that heaps of discarded horseshoes at a blacksmith shop where horses were of course reshod would have been a quite accessible commodity for this process.
Best regards,
Jim