I'll bet the micro bubbles I was talking about are left over divots from not taking the course to a fine enough grit. They are very tiny but they are there...........MrP
You know tumblers don't remove material by scratching, they remove material by abrasives rolling between rocks/glass like ball bearings and gouging.
This ball bearing rolling action digs tiny divots instead of scratching in a line.
Look at any rock/glass in coarse with magnification, you will never see a line scratch because they are not there.
There is no little man to hold an abrasive particle down and allow the rock to drag across to make a scratch.
Glass is notorious for carrying a fracture and those divots run a lot deeper in glass than they do in agate.
The problem is intensified because glass gets deep divots in 220 and 500 too. Not as deep as coarser grit but unusually deep non the less.
So it is up to you to roll or vibe it long enough to remove the divots.
To compound the problem glass gets divots from impact, but they will be on edges and points and easy to trouble shoot for that reason.
Where divots from abrasives will be equally distributed all over the glass.
This divot removal is not so easy to solve though. Easy to know why and talk big about it but removing them can be tricky.
I have no real remedy, I did modify my vibe to remove them easily but don't really know why exactly.
I can show you photos that is my gauge. A gauge that tells if they are ready for the vibe to remove them.
I use it regularly and it is trusty. It requires a certain angle of reflection and the same camera at the same distance with the same light.
The photo shows shadows created by divot depth, that simple.
I'll post them now. Maybe it will make sense.
These are acceptable shadows, left and right glass. Middle one is polished.
These shadows are blacker and defined(deeper divots). These(top 3) need further tumbling before going to vibe or else polish will suffer.
Lower ones are polished.