One job though that perplexed me was a very nice log home with brand new Pella windows. I used GG4 to do the job and it turned out nice. Then I get a call form the homeowner that their were some windows with marks running verticle in a very consistent pattern. I assumed it was maybe my squeegee blade so I agreed to come and look at it. I brought some Oil flo with me just in case it was some type of organic matter. I got their and cleaned both sides and it was still on the window. I wish I had a pic because I have seen this pattern before on heat tempered doors. It looked as if it in between the panes on the 2/3 side. But I could not fix the problem no matter what i tried. The oil flo actually made it look worse until i cleaned that off and used straight GG4. He did mention that he used vinegar to clean the windows but I doubt that was it.