I just did a demo for a property manager for water stain removal. The glass had been neglected for years and had heavy scale. I have attached some pics to see how heavy the stain was and the B4 and After of the plate I did for them.
On a side note, Be VERY careful with CC550. Besides being a health and property danger, It can damage the glass worse.
I was told by the property manager that their maintenance guy had been out there using CLR, Lime Away and muratic acid (all 3 are HCL, hydrochloric acid based) on the windows and could not get the white scale off. When I applied the CC550 in a corner, my fears were realized. The HCL based products had driven the stain into the glass and the CC550 reacted with it. It took the scale off and the glass was smooth, but it etched the scale patern into the glass and you could see it under direct sunlight, or the bright 500 watt halogen spots I was using when I did the demo. I had to go in after the building closed at 8 pm and work in the dark, the demo area was in a drive thru.
CC550 is a good product for stain removal under certain conditions, but you have to be able to recognize when and where to use it.
Oh...yes, we did get the job