From what I have read, Diamond Flint Glass Co. used only one diamond on their insulators before their reorganisation as Dominion Glass Co., which used two diamonds.
As this one has only one, I assume it is Diamond?
I think this is dark yellow olive?
From the Grand Rapids, Michigan, bottle show today. Given to me by a dealer when I purchased his 2-piece Brookfield transposition.
What would the age of this one be? 1910s?