This insulator and another like it (which has slight grayish tones) are believed to be unique and both were found in California during the late 1960s. Joe Maurath, Jr. is indeed fortunate to own this fabulous insulator which he received from Ray Klingensmith via one of his auctions a few years ago. It is entirely filled with zillions of microbubbles. The example shown has classic "Pennycuick" threads which are characteristic of being unusually sharp and concise, often with a "drip point" at the top of the pinhole. On August 11, 1885 James Pennycuick of Boston, Massachusetts was issued a patent "for forming threads on articles of glass". There was no mention within the language of his patent about insulators. Insulators of this style (all have "Pennycuick" threading) are not rare. Most are of aqua glass and have been located in many portions of the United States, so they enjoyed widespread distribution!