Found this on Cookscounty.com
Reducing the glaze to the right consistency takes a little practice. Too long in the pan hardens the glaze into a tacky mess, but not enough time means a runny glaze and diluted flavors. Here’s how you’ll know when it’s just right. (Avoid dark skillets, as you’ll need to gauge the changing color of the sauce.)
1. NOT YET The bubbles just break the surface of the glaze, and a spatula makes little to no trail.
2. NOW! The bubbles are smaller and more plentiful. The color deepens, and a spatula makes a trail.
3. OOPS! TOO FAR! Big bubbles cover the dark, thick glaze. A spatula leaves a wide trail.
Gourmet Dad, Don’t Let The Title Fool You 