On Sun, 27 Apr 1997, Shannon Dawdy wrote:
 
> This string on blacksmith floors has gotten me thinking.  I just excavated an
> area behind a plantation house (1765-1882) that possessed a strange stratum
> of rock-hard rust and coal concretions.  It took hours of chiseling to get
> through this ca. 8 cm layer.  Sometimes coming out in chunks, but never
> having any identifiable metal core, this presumed slag appears to be
> about 70% unidentifiable iron and 30% coal & clinker.
 
This sounds like corroded smithy floor debris. Originally it would have
been a mixture of fuel, hammer-scale, the odd small lump of slag and
occasional off-cut of metal. Or it is simply a hard-pan concretion due to
iron leaching out of the metal and slag in the context.
 
If you take a piece of the material, at look at it under a hand lens you
show find numerous small flakes of hammer-scale if it is the former.
However, if the material is very badly corroded it may be necessary to
mount the sample in epoxy resin and polish it for examination under a
metallurgical microscope to indentify the hammer-scale.
 
 
Chris Salter