The middle insulator is the only fake. Notice the red hue real he real purple pieces exhibit when sitting next to the fake blue-purple color resulting from a gamma-radiation altered insulator. As shown, the difference becomes very evident in a lineup. Also, the real ones glow a faint orange under a black-light, while most altered ones do not. The now fake purple piece was aqua to start and it DID glow under a black light, but after alteration it will not glow.

Both color and glowing characteristics as described are very good tests for determining fakes. However, since this picture was posted, it was discovered fake blue-hued purple glass insulator made by the California glass company WILL still glow under a blacklight.

The "Frustieri Test:" Collector Jim Frustieri discovered a good test for fakes: Look up through the pinhole. From this viewpoint, a non-altered insulator will pass light from top to bottom and through the base base of the glass a lot easier than an irradiated insulator. The irradiated ones' bases will look more dark b/c they the glass does not pass the light as well.