This month we will update you on a few interesting "finds" and reports. The insulators covered will be both unipart (U-numbers) and multipart (M-number) styles. To start, I thought it would be worthwhile to discuss briefly the use of Jack Tod's U-Chart as found in his book, Porcelain Insulator Guide Book. This is the primary reference for unipart insulators. In addition to the U-Chart, the book provides a detailed description of how insulators were made, manufacturer's history, and markings that can be found on unipart porcelain insulators.

Many people find using the U-Chart difficult. Most of these problems come from not understanding what the U-Chart is actually showing you and how to use it. There are relatively few CD numbers for glass insulators. Variations in a particular basic style (like signal, beehive, etc.) are not assigned a different CD, but in porcelain, a new U-number is often assigned when the differences are significant. Often the differences are characteristic of a specific manufacturer or identifies the dry process porcelain version. One exception is when the difference is primarily due to the trimmer operation that cuts the profile. Porcelain insulators are not pressed out in a mold, as were glass insulators. The only exceptions are when the complete shape of the insulator (with cable groove and/ or tie-wire groove) is cast in a mold or pressed in a two-part or three-part mold. The later method was usually for dry process insulators and certain smaller wet process porcelain styles made by Fred Locke and Pittsburg, which usually have visible mold lines through the tie-wire groove or mold line over the dome. Porcelain insulators that do not have mold lines had the profile cut out by an operator manually swinging a shaped trimmer blade up against the clay body as it rotates on a turntable. The trimming operation took no more than one second. 

The variability in profile of a specific insulator style could be quite significant when you consider there could be different trimmer operators and multiple trimmer lines. Additional variations in profile can occur when the trimmer blade becomes worn, new trimmer blades or made, the mechanism that swings the trimmer blade against the insulator becomes worn or misaligned, the young trimmer's helper didn't set the clay body in the center of the turntable, and probably other problems we haven't imagined. Then there are profile differences between months or years of production and between different manufacturers.

The greatest variability in profile, and consequently the most difficult area in the U-Chart for collectors, is the section that covers the "signal" style - U-228 to U-326. The next difficult area covers the small cable-top styles - primarily U-438 to U-488. 

Most people do not know that Jack Tod did NOT set up the U-Chart from actual specimens, but rather from manufacturer's catalog drawings. He did make drawings from actual specimens that were not represented in catalogs he had available. Actual insulators produced by a specific company did not necessarily match the catalog drawing profile very closely, especially in the early years before the early 1920's. During this period manufacturers could not turn out insulators fast enough and they had little concern over producing a consistent product. 

Remember, the dimensions shown for a specific U-number can easily vary by +/- 1/4" and larger amounts as the size of the insulator increases. Most of the questions I get concerning problems with matching specimen in hand with the U-Chart is that the dimensions do not match. The truth is the dimensions rarely will match exactly due to the reasons explained above.

Putting all this in words sounds complicated. It is about the same thing you do to ID a CD number, just you have fewer CD numbers to select from. There are over 1000 U-numbers. The U-Chart is logically laid out in order of basic styles: pony, exchange, mine, tramp, signals, cable-tops without petticoats, double petticoat, triple petticoat, high-tops, side petticoats, large styles, with the last section reserved for glazeweld, very early classics, and threadless. If you find a U-number close to what you have, do not get frustrated that it doesn't match exactly, because odds are few insulators will match exactly. For example, the photo of two U-250's illustrates the variability introduced by the trimming operation. Note the differences between the two insulators compared with the U-number drawing. If you think the variability is too great, simply call it Sim-U-250. That is close enough. If you give that description to someone else or put it on a sale list, others will know pretty much what you are talking about.

Two U-250's showing variability due to trimming.

Now to something more interesting n the new reports. Marty Caverly sent the following photo of his U-239 and U-191. These were made of dry process porcelain by R. Thomas & Sons Co. circa 1910. The glaze is a greenish gray in the thicker areas and the tops of the domes are "carved". Actually the top of the mold was carved, which leaves multiple flat areas as if the insulator itself was carved. This is a characteristic of Thomas dry process porcelain made through the 1910's. Both insulators were made in a 3-part mold. The body of the insulator with side cable groove was made in two halves of the mold with the top up from the upper wire ridge being the third part. I have one specimen of U-239 with almost no color in the glaze. Some specimens have a much more pronounced green color. Note the crude, porous nature of the porcelain. There are several "carved-top" styles. The greenish-gray U-191 is the rarest with less than 10 reported. Most have been reported coming out of Michigan.

Unmarked greenish-gray Thomas U-239 and U-191.

Apparently Locke was trying to compete with the cheap line of Thomas-made dry process insulators. Ken Willick reported finding a broken specimen of U-169 in the Victor dump. It was made of dry process porcelain with the large incuse Victor R=oo insulator logo marking and the glaze was bluish-gray.

Bluish-gray U-169 found in the Victor dump. Note the very porous dry process porcelain.

If you missed the San Jose National show this year, you missed a wonderful display by Barbara Smith and Carver Mead. Their collaborator, Alonso Rodriguez, recovered two incredible multiparts from the Guanajuato line in Mexico. The line was constructed in 1903 using Fred Locke M-3725's. The top insulator on the towers was vulnerable to lightning damage. The line was upgraded in 1906 by moving the top insulator below the double crossarm and running a grounded wire at the top. The insulators were also replaced with larger Thomas 3-part insulators. Alonso recovered one M-3990 (18 - 13 - 11 x 20.5) and one similar insulator that was assigned a new M-number. No specimens of either insulator have ever been reported. M-3990 was shown in the early Thomas catalogs. The new style is M-3940 (15 - 12.5 - 10.5 x 20). Note the smaller diameter top shell with unique style of crown that appears to be an improvement over M-3990 by strengthening the crown to make it less prone to damage. Both insulators have the period Thomas glaze that is reddish brown with drippy mustard in places. The top shell of M-3990 is mostly mustard colored!! The bottom two shells are nearly the same.

Thomas M-3990 and M-3940 from the Guanajuato line in Mexico.

You probably think that only glass insulators have drip points. Bet you didn't know that some porcelain insulators had drip points, too. How about a Fred Locke U-608A with "drip points"? Bill Rohde proudly displayed this unique specimen at the San Jose National. There are five rather large black "drips" along the outer skirt edge making a nice contrast to the caramel-colored glaze. I have the cousin to Bill's insulator. My U-608A has the same glaze coloring, but only one thick, black drip. Do any of you have a similar insulator with "drip points"?

Fred Locke U-608A with five large, thick, black "drip points".