Take a look at the National Insulator Associations's web site

http://www.nia.org/archives/referenc.htm

The standard work is the late Jack Tod's A History of The Electrical Porcelain In The United States, now out-of-print, I think, and his   Porcelain Insulators:  Guide Book For Collectors, 3rd Edition, which is still available.  See also his compilation of U.S. insulator patents.  Also Elton Gish's book on multi-part porcelain insulators, though these are less likely on archaeological sites.

I am currently researching early stoneware insulators including third-rail trolley and elevated railroad insulators.  The transition from wood to stoneware to porcelain was fairly rapid during this period and a little later.  Insulator collectors are an avid and very knowledgeable bunch but the emphasis is on glass insulators.
 
Jim Murphy

----- Original Message -----
From: Candace Ehringer <[log in to unmask]>
Date: Tuesday, August 7, 2007 1:15 pm
Subject: Ceramic/porcelain insulators

> Could someone please suggest a good reference for ceramic and/or 
> porcelain 
> insulators? Thanks!
>