Historically this and the other two blue Diamond-P insulators known have been referred to as "cobalt blue" however some refer to these as "sapphire blue". Take your pick! The August 11, 1885 patent on this insulator refers to "a method of forming threads on articles of glass" and was issued to James Pennycuick of Boston. There was no mention within the patent language about insulators. It is not known where these insulators (and the much more commonly found unembossed examples in this and other styles) were made. There is some strong speculation that they originated from a glassworks on Cape Cod. "Pennycuick" insulators have characteristic fine, concise and high quality threading which definitely was quite unusual for insulators of their day (c. 1885-1900).