There seems to be an ever-growing interest in porcelain insulators at shows. More dealers have porcelain on their tables and a wide variety is showing up on Ebay, too. It is great for those of us who look for something different. You may think that all possible markings on unipart porcelain insulators have been reported. I used to think that, but new markings have popped up in the last couple of years. Maybe the added interest in porcelain has people looking closer at their collection. In this issue of PIN we will show you the ones I have recorded over the past year or so.

I do not remember who reported the first marking, which was found on a U-447. It is actually an error marking. Note the L in LOCKE is upside-down. The "2" is the catalog number and the "V" indicates the insulator was made at the Victor, NY plant. Those made at the Baltimore, MD plant will not have a letter code in this type of marking.

Locke marking error on a U-447.

Dwayne Anthony reported the next marking on a U-3 and a U-65. The incuse marking shown in the photo was deeply struck on the top of the insulator. The two large dots may be rivets that held the LOCKE marking on the hand stamp.

Unusual incuse Locke marking found on U-3 and U-65.

Robin Harrison reported a U-202A made by Pittsburg with an incuse "356" on the top. In case someone is wondering if it could be the catalog number, this style was cataloged as No. 18. Note the very light colored mold line over the top, which shows up quite will against the blackish brown glaze.

A Pittsburg made U-202A with incuse "356" on the top.

Cooper Power Systems bought out the McGraw-Edison factory in Macomb, IL in 1985. They continued to make porcelain insulators until the late 1990's. The insulators were marked with blue under-glaze ink markings. 

One example was found on the new style, U-880A (see  Supplement 2001), which had a blue-gray "sky-tone" glaze and radio treated top with the following U-G ink marking:

The "M" and "E" represented McGraw-Edison with the year 1994 and the "2" indicating the second quarter of 1994. The "56-1" was the ANSI Class number. Later Cooper changed to a "CPS" marking dropping the use of the ME. I saw a U-735 on Ebay with the following blue under-glaze ink marking:

The "CPS" naturally represented Cooper Power Systems and the "55-4" was the ANSI Class number. I assume the "99" in the number represented the year 1999, but the number could have been the catalog number.

Two other markings on sky-tone glazed insulators with black radio treated tops were reported about two years ago. I'm sorry that I did not record the name of the person who reported them. The first marking is on an insulator similar to U-653:

The "86" is the year of manufacture. Joslyn insulators were made by Pinco in Lima, NY, which stopped making pin-types in 1987. The next double marking has been reported on several styles: U-425B, U-488, U-490, U-649, U-666, U-735, and U-737. The U-666 reported had this combination marking that includes the year of manufacture:

Jeff Hogan reported the next marking on a U-310. The black underglaze ink marking is on the skirt. It is like marking No.5 in the Jack Tod book, Porcelain Insulator Guide Book, except it also has the number "23" vertically inside an oval on the right. This is the year of manufacture, 1923. I checked Jack's file on Lapp and found a copy of a Lapp engineering drawing showing several marking designs. There were two sizes of markings like the one on Jeff's insulator. One of them is shown below:

The U-310 (in photo) has unusual under-glaze ink marking.. 
Note catalog number "591" and year "23".

It is odd that the catalog number shown on Jeff's insulator was "591". U-310 was Lapp's catalog number "591A". The "591" style was shown in the 1918 catalog, but not in later catalogs. It was probably replaced by "591A". The closest style to "591" in the U-Chart is U-309, but no one has reported a Lapp in that style. 

Jeff also reported an insulator with a very large incuse Lapp marking. The usual size incuse marking is 1/4" wide x 1/2" tall. The larger marking is 1/2" wide x 3/4" tall. Has anyone seen a Lapp marking this large?

Glen McAdam reported an interesting marking on the mine insulator U-94. It has the usual white glaze and embossed marking, THE. O.B. CO. MANSFIELD, O., around the pinhole. Glen noticed a recess-embossed Square D marking on the opposite end of the insulator next to the pinhole. Square D purchased the Peru plant in 1920 (operated as the Moulded Insulator Division), which made dry process insulators. The Square D trademark was registered in 1922 indicating use since 1914. Square D may have contracted with Peru to make insulators for them from 1914-1920 and as business grew decided to purchase the plant, which was expanded in 1927. (line drawing below)

Glen also reported a U-680A with a large incuse E" on the skirt. There are two sizes of "E" marking found on multipart insulators made by Thomas. Perhaps Glen's U-680A was also made by Thomas. Tom & Mary Miller reported getting one from Lu Farin's collection.

U-680A with large incuse "E" on the skirt.

Clint Gaylord reported a variation of the incuse Illinois marking that includes the year of manufacture. He has a white U-267 with the following incuse marking on the skirt:

ILLINOIS
1953

Shaun Kotlarsky reported an unusual Ohio Brass marking on a U-368. The glaze is an early mottled gray color. Usually these have an embossed O-B on the edge of the crown. This typical O-B marking is engraved in the mold so every insulator is marked. It is the only embossed marking found on wet process porcelain insulators. However, Shaun's U-368 does not have this embossed marking. Instead, there is a deeply struck recess-embossed O-B marking on the skirt! We can only assume that this insulator was made just prior to the crown marking being cut into the mold. I would guess Shaun's insulator was made around 1907-1908. Ohio Brass bought out the Akron HP factory in 1907 and soon began using the crown marking. This specimen of U-368 was probably made shortly after the purchase of the factory. (Pics below)

U-368 with unusual recess-embossed DB marking on the skirt.

There is one last marking to report. It is a bit ho-hum for interest, but we may as well mention it for completeness. The Gould logo marking has always been an incuse marking. That seems like a rather odd marking method for a modern line of insulators made from 1977-1981. The more typical marking method would be under-glaze ink. Perhaps started near the end of their production, Gould did indeed use an under-glaze ink logo marking.

The u-g ink marking has been reported on U-832 and U-880A. (below)

I'll bet not many of you have seen the large incuse P.R.R. marking, which is rarely seen on U-179. I haven't seen one in many years and surely don't remember seeing one this clear. You can see from the photograph that the marking nearly covered the top of the insulator.

U-179 with large incuse P.R.R. marking