Share your favorites on Show & Tell

Kerr "Cobalt Splotch" Insulator

In Tools and Hardware > Insulators > Show & Tell.
Recent comments96284 of 133124Rare light blue Gunnar Nylund vase - Strombergshyttan mid 1950s.Andrea by Sadek tea pot? Rare or hard to find?
Love it
Like it

epson233epson233 loves this.
old.bottleold.bottle loves this.
miKKoChristmas11miKKoChristmas11 likes this.
VikingFan82VikingFan82 loves this.
DMK678DMK678 loves this.
ChapeldreamerChapeldreamer loves this.
SerenitySerenity loves this.
potreropotrero loves this.
See 6 more
Add to collection

Please create an account, or Log in here

If you don't have an account, create one here.

Create a Show & TellReport as inappropriate

Posted 7 years ago


(1 item)

This is an unusual gray-area insulator: it's not quite "factory" but it's also not "fake". It was made in 1972 at the Kerr plant by factory employees on factory equipment with the blessing of the company, but it's not a production insulator. The story is that the employees had intended to produce a pure cobalt insulator, but oops, they forgot to turn on the stirrer! However, Kerr had previously produced cobalt splotch commemorative Mason jars in 1968, so the splotches may have have been by design.

Richard Wentzel, Millville glass expert, says "The cobalt was hand introduced into the feeder. It was crushed cobalt glass. The mechanism which would have stirred it properly into the glass stream did not get turned on, so instead of a solid cobalt colored CD 155, you got just a splotch" (where the little pieces of frit moved in the glass while the glob was processed into an insulator).

The color chips looks like concentrated frit to me instead of pieces of cobalt cullet: they are black, and leave rich cobalt streaks in their wake. If they were pieces of cobalt glass, they would be cobalt colored, not opaque black.

It is believed that from 100 to 150 were made. They are very popular today and sell in the $750 to $1,000 area. When first made, they were brought to an insulator show and offered for $5 but there was little interest at the time.

While cobalt is always an attractive color and they would have been welcome in pure cobalt, I find the streaky version ever better: each one is unique! And talk about contrast!

You can read more about this piece in "History of the CD 155 KERR DP1 Cobalt Splotch" here: <>


  1. potrero potrero, 7 years ago
    Anybody who wants to experience the visual beauty of glass insulators and learn more about them should visit Ian's website, Glassian, and also read the Collectors Weekly interview with him. You can get to both via this page:
  2. Laura, 7 years ago
    Its great! I worked at the Kerr Glass plant a little before 72 in Plainfield Il. Thanks for sharing
  3. imacky, 7 years ago
    Kaileys-- I can't believe the story is just as they say. I *have* heard about collectors who, for a lark, put some unusual piece of glass up on a pole where they know some other collector will be looking-- for example a clear dirt-common Hemi-42, but stained bright red.

    The cobalt splotches were made for collectors, and originally brought to a show for sale. They're not going to accidentally end up in a carton of production clear ones somehow.

    Noope, can't believe it. Maybe someone put it up there knowing another collector was working the line, just to mess with him (assuming there's even a grain of truth to the story).
  4. old.bottle old.bottle, 4 years ago
    i never knew that they made cobalt insulators

Want to post a comment?

Create an account or login in order to post a comment.