Collectibles--General (Modern)/glass insulator


QUESTION: hi bob.
i found an insulator that still has a metal l-shaped mounting bracket. i can't separate them as i am afraid i will break the glass. this insulator looks like it was a practice run. the lettering is all on the top, above the groove. there are streaks and striations in the glass that i thought at first were a design, but i now i think they are flaws. the glass is pale green and heavily bubbled. the lettering is difficult to read but i have been able to get the following:

row 1 : JULY 25 1865
row 2: PAT JULY 25 1870
PAT P --- 65      FULTON NY

the bracket is rusty but still has a heavy coat of paint. there is a lot of paint on the insulator too.


ANSWER: Hi Nancy --

Your insulator sounds like an early Brookfield product.  It is probably also marked W. Brookfield, but the embossing is too faint to read.  You are correct to be cautious about removing a pin, especially a steel one.  There are several styles with similar markings that date from the 1870s so if you could attach a picture I should be able to identify it.

If the pin is a metal one, I have had luck using liquid wrench or WD-40 to loosen the rust and slowly work the pin loose by twisting the insulator back and forth.  I have also used muriatic acid to remove steel pins, but this is nasty acid and must be done out doors.  

Brookfield was the first glass maker to make threaded insulators -- and the patent for threading is the July 25, 1865 date on your piece.  Their office was located at 55 Fulton St. in New York City at the time dating that insulator to the 1870's.  If there are really a lot of bubbles in the glass, it will increase the value.  Glass making at the time was a pretty crude process, and there are typically fold lines and other flaws in the surface of the insulators.  If you can attach a picture it will let me identify the insulator for you and also give me a better idea about the pin.

         Thanks, --Bob

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QUESTION: hi bob

thanks for your reply. i took several photos but i will have to figure out how to post them. i will try but will probably have to go to tech support so it may take a while.


Hi Nancy --

The photos came out fine!!  Your insulator is a Brookfield style -- Insulator collectors have come up with a numbering system for the various styles called the Consolidated Design or CD numbering system.  Yours is a CD 133 which was a popular style in use from the 1870's through the turn of the century.  Although very old, these are actually pretty common with a $3-$5 valuation because so many survived until the present.  Here is a link to more information about CD 133 and the CD system in general:

CD 133 =

CD numbers =

As for the pin, if it is not cemented in I think with penetrating oil you can probably work it loose -- if it is cemented Muriatic is the only real option.  For that use caution and do outside away from people -- the fumes are pretty strong and will rust anything they come in touch with.

         Thanks, --Bob

Collectibles--General (Modern)

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Bob Berry


Questions related to collecting Glass Insulators and porcelain insulators - I can provide historical information as well as current collector values. I am also interested in purchasing insulators I need for my collection.


I have collected since the early 1970's and have much historical information, as well as knowledge of current insulator values.

National Insulator Association (

BS & MS in Electrical Engineering

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