Met History wrote:

> (cross posted by Christopher from Preservation-L) [or, is it
> Preservation-Hell?]
>
> The iron spot is not introduced.  It is a component of the clay from
> which the brick is produced.  The firing process brings out the color,
> and it is normally darker on a darker (longer fired) brick.  The
> metallic component that contributes the black spots is reported as
> Iron Pyrite, or sometimes as Manganese.  I am not sure which is right,
> possibly both. Pyrites are sulfurous, gold in color, and Iron Pyrite
> is also known as "fool's gold."  No relation to your problem, I presume.
>
> Since the black spots are a natural component of the clay, they are
> consistent within the mixture and occur throughout the brick.
>
> Robert Parker Adams, Architect
> ([log in to unmask] <mailto:[log in to unmask]>)

Not so sure I agree with the "not introduced" aspect... natural
formations would be erratic thus not always consistent in a run of brick.
If not introduced... then a geological question as in how come only iron
spots occur and say no quartz or other pebbles?
Iron spot brick tends to date to an era of industrialized brick
manufacture, thus mechanization of the process and a mind-set elevating
consistency.
I'm also not so sure pyrite is the culpret. I know damned well what
pyrite is. Iron is highly prevalent and available.
You don't see the brick so much so often any more... did they run out of
iron spotty clay?
Clay, with or without the measles, comes out of a hole in the ground and
should be able to be traced to point of origin.

][<

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