Telegraph Insulator

A delightful Telegraph line piece I picked up for $4. The Hemingray No. 40 is one of the most commonly seen insulators put out by Hemingray, but they are almost always seen in a shade of blue-aqua or blue-green (See pic, where it is compared to two other insulators, the left being an aqua version, the right being a blue-green Brookfield with ghost embossing.)

Although No. 40's (CD number no. 152) come in green, it's a bit harder to see one swirled with amber.
Because the amber is more evenly distributed than usual swirls, it turns this piece from an emerald to more of an olive color.

Color can be accidental (such as that something got mixed in incorrectly,) or it's what was cheapest at the time-- "Attention all buyers: Such and such has a great deal on green glass!"
Mine is likely chromium mixed with tin-oxide and arsenic or iron-oxide.
Sulphur or sulphur/titanium is also mixed into the glass, and that makes the amber in it.

See more on it here, and see where my questions are blown over on it because of the Brookfield piece:
http://www.antique-bottles.net/forum/CD-152-in-Green-with-Amber-Swirls-and-a-Lapp-1930-Porcelain-m683381.aspx