I imagine you have Googled the word as well, Robert, but here's a clip I found. Another reference was to the material used as an insulator in a light bulb and mentioned "...or other refractory material". I would assume it was a hard compound containing asbestos that would not decompose at very high temperatures.

I believe the "vulcan" part of the word is related to fire, and not to vulcanized rubber, which is a completely different material, one that requires fire (high temperatures) in its manufacture.

Research Division

Reprinted from "INSULATORS - Crown Jewels of the Wire", November 1976, page 34

Dear Dora:

Ref the insulator on page 32, Aug '76 CJ, here is the light you wanted shed on the marking.

The insulator is Patent #520,602, May 29, 1894, Henry H. Luscomb, Hartford, Conn. (As you state, this patent is shown in Brown's "Unique", page 27.)

Luscomb was an employee or officer of the Johns-Pratt Co., Hartford. He had other patents beside this one, some of which were assigned to Johns-Pratt.

My crystal ball therefore suggests the complete marking on Harold's specimen would read:

THE IRON CLAD POLE TOP
MADE IN U.S.A.
THE JOHNS-PRATT CO.
HARTFORD, CONN.

The histories of the related companies (H. W. Johns Mfg. Co., H. W. Johns-Manville Co., Johns-Manville Co.) are briefly given on page 168 of my book.

The subsidiary Johns-Pratt Co. was organized in 1886 for the manufacture of products from Vulcabeston, and later Moulded Mica (of Gould & Watson Co.). Johns-Pratt (and later Johns-Manville) for many years sold an extensive line of pin type and strain insulators made of these materials.

It would be great if one or more collectors really worked at it to form specialized collections of all these "composition" insulators made by Johns-Pratt Co., Electrose Corp. and others. We have the company histories and catalogs. It would be a shame if the specimens got lost in the shuffle as time marches on.