My first week on the job I tried to clean all the mirrors in my system- I used the 'drop and drag' method... I put a lens cleaning tissue on a silver coated mirror and put a drop of ethanol on it, I then dragged the tissue slowly off the mirror- the pumice dust severely scratched the mirror beyond repair- I had to replace it. The pumice dust sticks to surfaces in a way that defies belief....

The output lens of the laser is COVERED in pumice dust, apparently we are about to take care of this problem using Opti-clean, but you would be stunned at how that dust refuses to go away with washing...

The humidity is not all that low, we have had the output lens frost over in the middle of the night- I have had to go up and use a heat gun on the lens to clear off the frost- the frost seems to make the dust cling on the surface...

:) heating a $50,000 piece of glass with a heatgun is NOT a way to relax...