You have probably already noticed Bill Rohde's beautiful photograph on the cover. Maybe you haven't noticed the concentric rings under the top skirts. Both insulators are M-4415 made by Thomas around 1905 to 1912. We know Thomas made them during this time period because they have the characteristic Thomas "blue jean seam" inside the bottom skirt. This distinctive mark in the clay was caused by a section of denim pants leg placed inside the skirt when it was pressed out in an apparent method to prevent the plunger from sticking to the damp clay. The heavy seam of the denim pants leg is usually plainly visible and many insulators also exhibit the fine crosshatch of the denim material, too, if the glaze is not too thick. We haven't found a Levis label on one yet.

Cover Photo

Illustration from patent No. 838,163 granted to 
Frank Baum on Dec. 11, 1906.

Frank G. Baum was granted a patent for the concentric ring feature on December 11,1906 (838,163). On the previous page is the drawing from the patent. Note that the concentric rings were not shown on the top skirt, but rather on the second and third shells. There are four long petticoats provided under the top skirt. This is the first reference to petticoats used under the top skirt on multipart porcelain insulators. The petticoats and concentric rings added length to the leakage path across the surface of the insulator, thus providing a greater resistance. The odd ribbed tubular insulator on top served the same purpose of adding to the leakage path, but it was suggested that the surface would be easily washed by rain.

Don't confuse Frank G. Baum with the author of the 1908 book "Dorothy and The Wizard in Oz" - that was L. Frank Baum. This is Frank G. Baum, a resident of San Francisco and an electrical engineer. His first project after graduating from Stanford in 1899 was to assist Dr. F. A. C. Perrine in the design of an installation for Standard Electric Company's Electra Powerhouse on the Mokelumne River in northern California. He also worked as consultant to the Bay Counties Power Company. Both companies constructed power lines in northern California that used the Fred Locke M-2795 extensively to carry power to San Francisco and the surrounding area.

Baum suspension insulator patent assigned to Westinghouse.

M-2795 was unique in that it had a porcelain top with eave gutter and spout and a glass bottom. He later worked four years for California Gas & Electric and opened his own consulting office for a time. He was then a consulting hydroelectric engineer for Pacific Gas & Electric Co. (PG&E). In 1921, he supervised the design and construction of the Pit River development in the Shasta area of northern California. Power was transmitted at a record 220,000 volts 202 miles away to Oakland. The insulators used on that power line could be the suspension insulator in Baum's patent No. 1,768,948 granted to him on July 1, 1930. On the previous page is part of the patent drawing. The patent was assigned to Westinghouse, but note that the patent application was dated December 3, 1921. This may very well be the basic design used at Pit River.

Now back to the first Baum patent. A couple of years ago, Paul Greaves and Mike Spadafora discovered a new multipart style in northern California. It was discovered after my new book, Multipart Porcelain Insulators, was at the printer and too late to make it in. I assigned it M-4604. After several searches on two lines in northern California, they ended up with about 5 specimens most of which had to be kitsulated. I believe only one was found whole in nice condition and I believe they told me all of them have the incuse marking, LIMA, N.Y., on the crown. They also thought another similar style was used that did not have the flared bottom skirt. As you can see in these photos, M-4604 has four long thin petticoats under the top skirt exactly as shown in Baum's first patent! This undoubtedly was the first insulator made from the Baum patent. Lima was in operation only from 1904 to 1908.

Paul Greaves' photo of M-4604 with incuse 
marking, LIMA, N. Y. Note the four long thin 
petticoats under the top skirt. The fourth 
petticoat is next to the cement joint and 
difficult to see.

Evidently the concentric ring feature was used next. I suspect Lima had difficulty making the long petticoats and Baum decided to use his concentric ring idea instead. Apparently Lima was not able to form the concentric rings in the second and third shells. The next insulator Lima made for Baum was probably M-4600. Lima even cataloged this style in their first catalog along with the identical style, M-4600A, but without the rings. M4600 has 13 rings under the top skirt. It is a rare style. Only 8 are know unmarked and 5 reported with incuse marking, LIMA, N. Y. This insulator is a well-made insulator in stark contrast to M-4604. Paul and Mike found both M-4604 and M-4600 on the same line. 

The factory of Lima Insulator Co. was destroyed by fire in 1908. Evidently Baum turned to R. Thomas & Sons Co. to produce an insulator similar to the M-4600 he was getting from Lima. In fact, at least one unmarked Thomas M-4600 is known and it is in Bill Rohde's collection. This specimen has 11 rings. We do not know if this is the first insulator with rings Thomas made or maybe this particular specimen was produced later since the glaze color is darker without the mustard color seen on earlier Thomas insulators. 

At any rate, Thomas must have had the exclusive right to the ring feature. They made four styles with different numbers of rings. Below is a summary of the known ringed styles:

M-4325C (Thomas): 9 rings

M-4382 (Thomas): 10 rings

M-4415 (Thomas): 5 rings 
M-4415 (Thomas): 6 rings 
M-4415 (Thomas): 10 rings

M-4600 (Thomas): 11 rings 
M-4600 (Lima): 13 rings

Most of the Thomas insulators found with rings (except M-4600 which has a dark brown glaze) have the early glaze that is a beautiful combination of mustard and reddish brown. These are some of the most attractive early multipart insulators. Note that all the ringed styles are four part styles with recessed fourth skirt. The ringed insulators have been found only in California. Collectors have captured a few ringed multis over the past 10 years and they are probably all gone now from the lines. I believe that Bob Jackson was the last person to retrieve a couple of these beautiful and very desirable classic multipart porcelain insulators as late as 2002. If you want to see what some of the ringed insulators look like in color, go to my web site: http://www.r-infinity.com and click on the link for the Baum Ringed Multipart Insulators.

Unmarked Thomas M-4415 (left) 
and M-4382 (right) each have 10 rings.

Bill Rohde's unmarked Thomas M-4325C with 9 rings.