Friday, February 4, 2011

Insulator Post -- Brookfield Baby Signals

Here is a pair of Brookfield Baby Signals I recently acquired from an online vendor. 

These insulators got the nickname "Baby" because they are the smallest of the signal style shape.  These two pieces produced sometime before 1922 stand 3.125" inches tall and both have an outer diameter of  2.875" inches.  Of the many glass houses that made the baby signal I now have examples from Brookfield, Hemingray and the California Glass Insulator Company.

Embossing- front skirt:  BROOKFIELD
rear skirt:  NEW YORK

Embossing:  No 32       B

I took advantage of the clear skies and set up in the back yard using the late afternoon sun to illuminate the glass.  Although I was hurrying due to the temperature of 25 degrees and a bitter cold breeze I think the pictures turned out fairly well.  An interesting effect is the shadow which adds a little depth to the images.

What looks like a chip in the glass at the base of the No 32 B insulator is actually a smooth underpour.  There was not enough molten glass to fill the mold at this particular area so the glass settled and dried with a smooth radius.  A small flaw like this would pass quality control inspection as it would not hinder the insulator's ability to do it's job. 

Another feature in the photographs are the serpentine "straw marks"  or shallow grooves visible on the dome above the shoulder on each of the insulators.  I don't know of the cause of this phenomenon but my guess would be that the curvy channels were carved out by escaping gasses while the glass still thousands of degrees was forced under pressure to take on the shape of the mold.  Details like this add uniqueness and character to these colorful pieces of telecom history . 


  1. Good guess on the straw marks but here's an answer from

    * What causes creases and lines ("straw marks") on insulators?

    Creases and lines are caused when the glass being poured isn't hot enough to melt back into itself in the mold. These are sometimes referred to as 'straw marks', 'straw lines' or 'cold mold' and are lines in the glass surface where cooling has occurred during the pouring and the pouring stream did not completely melt back together during the pressing of the insulator. The liquid glass folds over itself as it fills the mold and the creases are hardened in position when they touch the sides of the mold. The glass does melt back together on the inside, but because the outer glass is contacting the (cooler) mold parts, the glass can't retain the heat needed to completely fuse back together again on the surface.

    'Cold mold' is something entirely different. If the mold is not at least 1000 degrees F., then the glass stream entering the mold will cool instantly as it flows over itself. This causes a concentric rippling effect, much like throwing a stone into a pond. They are occasionally seen on the domes of insulators, but are not caused the same way as creases and folds in the glass.

    The parallel thin lines which are often seen over the dome and down one side of an insulator are from a long thin 'stringer' which enters the mold before the rest of the pour. This only occurs when multiple insulator molds were being filled from the same ladle, because the glass never actually breaks clean at the end of a previous pouring. It just hardens with a little thread on the end, which becomes the first part to enter the next mold as the pouring begins again. This is evident on lots of HG signals and on lots of Brookfield products too. The thin parallel lines can be followed until they branch away from each other. This is the point where the hardened stringer on the bottom of the pour is attached to the hotter contents of the ladle.

    Later, with automatic portioning machines, the glass stream was cut or sheared off for each mold filling. This often left a shear mark about 3/4" long somewhere on the bottom of the mold (on the dome). Lots of the later era glass insulators have this marking on one side of the dome, like Dominions, Whitall Tatums, Armstrong, etc.

  2. What is the CD number for the Brookfield one???

  3. All baby signals, no matter the manufacturer, are classified as CD160s (Consolidated Design number) in the hobby.