From the manufacturer:
StarBrite Ancient Slate was mixed by Ink Master Season 4 Winner and Pro-Team artist, the late Scott Marshall.
This color is a dark, blue-ish grey used to lay down a solid base without black if you prefer. Blend Murky Tomb off of that for smooth blends.
Ancient Slate is a great color that brings a lot of depth when working on metallic looking pieces or stone.
Gauge Size
The gauge size is the circumference of the smaller bar in the middle.