This from Tim Scarlett at Michigan Tech, who is coauthoring a brick
identification guide for Left Coast Press, Inc.


> 
> The indentation you describe is called a "frog" and it is indeed  
> caused by the molding process.  Bricks with frogs are typically
> "soft- 
> mud" manufactured, which means that very wet clay was slopped into a 
> 
> wooden or iron mold with four sides and a bottom.  The bottom of the 
> 
> mold surface also included a raised area that impresses the clay when
>  
> it is forced into the mold.  The back of the mold is then "struck"  
> with a blade or wire.  The strike creates the sixth side of a soft- 
> mud molded brick.  You can often still see the strike marks on the  
> opposite side of the brick from the frog.  If those strike marks are 
> 
> irregular, meaning that they appear to have been formed at non- 
> uniform angles, then the brick was probably hand struck while in the 
> 
> mold rather than by some automated process.
> 
> The frog presents a couple of advantages- it creates a recess for  
> mortar, it makes each brick weigh just a little bit less, makes each 
> 
> brick a bit thinner so it fires more throughly, and it takes slightly
>  
> less clay to make each brick.  While the difference seems trivial for
>  
> each brick, multiply the difference in weight and cost by the 10 or  
> 100 thousand bricks in a large building or the millions of bricks  
> made annually in a large yard, and you can see how the savings do  
> indeed accrue!
> 
> The bad news is that this information does not necessarily yield a  
> simple probable date of manufacture.  That is a much more complex  
> problem.
> 
> You can find more information in Larry Gurcke's 1987 book, Bricks and
>  
> Brickmaking: A Handbook for Historical Archaeology (Idaho).  Keep an 
> 
> eye out for the second edition of this text from Left Coast Press,  
> updated and revised to include much more chronological and regional  
> information!
> 
> Best,
> Tim
> 
> Timothy Scarlett
> Assistant Professor of Archaeology
> Industrial Heritage and Archaeology
> Department of Social Sciences
> Michigan Technological University
> [log in to unmask]
> (906)487-2359
> (906)487-2468
> ------------------------
> Currently conducting fieldwork at the site of the West Point Foundry 
> 
> in Cold Spring, New York.
> 
> 
>

Mitch Allen
Publisher
Left Coast Press, Inc.
1630 N. Main Street, #400
Walnut Creek, California 94596
925 935-3380 phone and fax
[log in to unmask]
www.LCoastPress.com

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