Hi all! Recovering from a frustrating night in the workshop and thought this group might be able to help.  We are working on engraving 11oz whiskey glasses. Our sample one was perfect. We are using cermark spray to prep the glass and using 70 power/50 speed.   We could not get a good result.  We put a dark sock inside the glass, painted the outside and inside of the glass, switched to acrylic paint, and it only kept getting worse.  The last two attempts didn't engrave into the glass at all.  

So, two questions:

1. What is your favorite/best way to make the glass for engraving?
2. Does long run times or other things make the laser lose power? We've only had it a year, and it hasn't been used heavily.

Thanks much!