Very little was known about U-936 when an unmarked specimen was reported by Evelyn Anglin in January 1973. Jack Tod was aware of this 2-part glazeweld style from the 1907 Thomas catalog, but the illustration in the catalog was not sufficient to make a drawing for the U-Chart. It did not appear in their 1904 catalog and obviously introduced around 1907 with catalog number 2013. All the other glazeweld styles that were shown in the 1904 catalog were given new 4-digit catalog numbers, too. U-936 could be ordered with either a 1" or 1-3/8" pinhole and it was designed to be used for up to 25,000 volts. The Anglin insulator had a 1" pinhole, and I believe all the U-936's located so far also have a 1" pinhole. When we did the survey of about 30 porcelain collectors for the Value Guide, 8 unmarked U-936's were reported and only one with an incuse THOMAS marking on the ear. Later it became obvious that these had been found in the southern California area. 

A couple of years ago Mark Johnson found three U-936's on the same pole in southern California! Two were unmarked and one had the THOMAS marking on an ear. However, Mark said that one of the "U-936's" was different. It was in fact a fraction taller and a full 1 /2" smaller in diameter. And the top skirt was much thicker! Mark shipped the insulator to me for closer inspection (thanks Mark!!) and to make the drawing for a new U-number. It has been assigned U-936A. It is unmarked but definitely a 2-part glazeweld made by Thomas. I feel sure U-936A was made after U-936 because the skirt is so much thicker. Even though U-936A is smaller, it weighs essentially the same (2-3/8 lbs) as U-936 due to the-thicker skirt. When U-936 was introduced, thick porcelain was difficult to make. Boch was granted the 1898 patent for Thomas' "glazefilling" process, which produced larger insulators by fusing two or more thin shells. Only Imperial had the skill to make thicker porcelain although it was fraught with large air bubbles. Insulators made with the glazewelding technique was continued by Thomas in their 1907 catalog, but soon dropped in favor of using Portland cement to hold shells together.

A photo by Mark Johnson shows the U-936A 
still in service. It is in the middle, and 
notice the porcelain high voltage sign.

U-936A (left) and U-936 (right)

U-936A (left) and U-936 (right)

A new manufacturer of pin-type porcelain insulators has been discovered, but I do not know of any specimens that have been confirmed as having been made by them. I need your help in identifying specimens that may have been made by this company. The company is Davidson Porcelain Co. of East Liverpool, OH. I located one undated catalog for this company and one 1918 catalog for Davidson & Stevenson Porcelain Co. According to Jack Tod's book, Electrical Porcelain, the plant was located on the north side of Newell Rd. at Corporation Line, Newell, WV, but they used an East Liverpool mailing address. East Liverpool was across the Ohio River and the center for porcelain manufacturing. Photographs of the factory indicate it was located in Chester, WV, which is a couple of miles east of Newell.

Abandoned factory of The Davidson Porcelain Company.

The Davidson & Stevenson Porcelain Co. was founded in 1913 (catalog says 1914) to make specialty porcelain (non-pin-types). They leased another pottery plant at the northeast corner of Broadway and 6th streets in East Liverpool from 1913 to 1919. This plant reverted to Hall China Co. in 1920. When Stevenson left the company in 1920, the name was changed to The Davidson Porcelain Co. Operations were suspended in 1936. They primarily made specialty porcelain (knobs, cleats, spools, etc.). Insulators from the earlier operation were embossed "D & S", "D & S P Co.", "EVER READY", or "EVER READY / D. P. Co.". The specialty porcelain insulators would have been made of dry process porcelain. 

The 1918 catalog does show six pin-type insulators for low voltage and distribution service up to 10,000 volts. The illustrations are I an upwardly tilted profile to show the inner skirt, so a possible unique profile is not obvious. The six styles are exchange, pony, signal, two cable-tops, and a beehive. There is no indication that the pin-type insulators were either wet process or dry process. It stands to reason that if they had been made from wet process, the catalog would have noted such to make them stand out among the many styles of dry process specialty porcelain. D & S could be the mystery company who made the dry process U-151 A with unique, often black and tan, shiny glaze. The dimensions and upwardly tilted profile match exactly! It should be noted, too, that Thomas (a neighbor to D & S) made several small low voltage styles during this same time period of dry process porcelain.

The undated catalog of The Davidson Porcelain Co. (Bulletin No. 131) offered a completely modern array of double and triple petticoat insulators along with the basic smaller styles. Nowhere in the catalog does it mention that they were made of wet process porcelain but I am sure they were. The various triple petticoat styles would not have provided satisfactory results if they were not wet process. Another indication is a guy insulator was offered in either wet or dry process, which implies that all other insulators in the catalog were wet process.

The Davidson "high tension porcelain" insulators had a very unique and distinctive profile totally unlike those made by any other manufacturer. Please review the six styles shown here and see if you have anything similar in your collection. I would like to identify at least one style so we can begin to identify characteristics that would help to identify other commonly styled insulators made by D & S.

Davidson claimed their "Balanced Design Insulators...have been styled not to be different in visual appearance but primarily to provide greater physical strength." In addition, "The graceful lines of Davidson Porcelain Insulators have other useful features. They are self-cleaning. Soot and dust will be washed off with every rain. The lineman has greater freedom in making ties. There is no likelihood of the cable slapping the porcelain skirts." They conclude with, "They are manufactured carefully from only the best raw materials obtainable, and under the supervision of experts for an important service. They are not cheaper - but better - and last longer." The unique profiles of these six insulators should make them easy to pick out from the crowd. Note the straight skirts extending down at a 45-degree angle and the unusual profile of the smallest cable-top. If Davidson did make these insulators for several years that closely match the catalog illustrations, surely some have survived and have found their way into collections. Again, let me know if you have something close to one of these.