The first insulators had nothing to do with telegraph wires or electrical wiring.
They were the glass insulators that were used to protect homes against lightening strikes.
The National Insulator Association, A 501c3 charitable organization, is an international organization of collectors and friends interested in communication and electrical insulators, as well as other artifacts connected with insulators, such as telephone, telegraph, power transmission, railroads, and lightning protection devices.
The NIA also has a strong focus on research and education on insulators, the companies that used them, and the companies that made them dating back to the mid 1800's.
Flaws can include cracks, bruises, chips, nicks, dings, scratches, wrinkles, wear (from abrasion), and even inclusions, such as debris within the glass or ceramic.
Except for a surfaced bubble that causes a chip (after manufacturing), internal bubbles are not considered to be flaws due to their common occurance. The Fleron company was in business from 1922 to 1941.
In conjunction with the expansion of rural electrification in the early 20th century, there was a major boom in the manufacturing of insulators, peaking from the 1920s through the 1940s with production in the millions per year.
Commonly made from glass or porcelain in a dazzling array of shapes and...
* = Microflaws are aged (not manufactured) defects that are not obvious without careful and close visual inspection.
These tiny flaws are so small that they do not normally distract from the aesthetic appearance of the artifact.
Similar to their glass counterparts, porcelain insulators date back to before the Civil War for telegraph wires.