On Wed, 30 Apr 1997, Early American Museum wrote:
 
> About hammer scale vs products of iron corrosion, hammer scale is extremely
> thin and fragile in my experience. The excavators of the John Deere
> blacksmith shop (c. 1840)  at Grand Detour, Illinois commented on finding an
> area of red stain around the anvil but there was no slaggy or crusty layer
> present.  The hammer scale I am familiar with from forging activities is
> thinner than mica platelets for instance, and flies around at a hammer blow.
> It is fragile and not at all resistant to any kind of mechanical force like
> being stepped on and will often crumble when being brushed of an anvil or
> trip hammer die.
>
        Yes, it is fragile on the macroscopic scale, but once it is down
to a few millimetres across it is mechanically stable. At Maiden Castle,
Dorset the hammer-scale, charcoal and slag had built up on the floor of
the forge hut to a depth of at least 120mm. From our sampling there was
at least 200 kg of scale in the hut.
The scale was virtually indistinguishable from the stuff coming off my
anvil, even though it had been in the ground nearly 2000 years.
 
However, at Dudley Castle the forge floor was virtually fully corroded
after only 300 years, but in that case coal had been used as the fuel. The
sulphur in the coal speeds up the corrosion process.
 
 
The thickness of the plates seems to be a function of the temperature at
which it formed. Thus the  first scale from welding and bloom
consolidation can up to 0.5mm thick if it is a pure scale (oxidized iron,
and even thicker if there was a contribution from the slag in the metal or
flux.
 
As well as the plate hammer-scale, these deposits also contain lesser
amount of small (0.1-5mm) spherical slag particles formed by the mid-air
of solidification of slag sprayed out from the surface of the metal by the
action of the hammer.
 
 
>
> >
> >How is hammer-scale defined, and what are the ways of telling the
> >difference between it and the normal flakes of de-laminating iron
> >associated with corroding artefacts that one generally finds in
> >excavations?
> >
 
If uncorroded the hammer-scale can be separated out magnetically. If
corroded, it usually retains its distinctive platy character when viewed
in polished section. The spherical particles again are distinctive, but
more susceptible to weathering.
 
Yours
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