This is topic Projection Port Glass Cleaning. in forum Film-Yak at Film-Tech Forum ARCHIVE.
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Posted by Robert Maar (Member # 578) on 01-21-2001, 10:57 AM:
Have you ever noticed how dirty the projection port glass looks from the auditorium side, when the projector is running. Does anyone have a solution for keeping this glass clean.
Posted by Darryl Spicer (Member # 711) on 01-21-2001, 11:32 AM:
If you can reach the other side. Use some glass cleaner and paper towels.
Posted by Brad Miller (Member # 2) on 01-21-2001, 01:11 PM:
Get yourself lens cleaner, McDonald's napkins and a small 2x4 inch sanding block from a hardware store. Using 3-4 napkins at a time, wrap them on the sanding side of the block and douse the napkins fairly generously with lens cleaner. Wipe the inside of the glass with medium pressure (nothing strenuous) in a vertical motion. Then IMMEDIATELY take a few more napkins and lay them on the sanding block and press HARD on the glass to wipe it dry, again using vertical strokes. Repeat this procedure for the auditorium side, but wipe this one in a horizintal fashion. Then turn on the projector and xenon with no film in the projector and take a look at your glass. If you see any vertical streaks, they are on the inside of the glass and you can generally touch them up with a dry napkin. If the streaks are horizontal, they are on the outside of the glass and again you can generally fix it with a dry napkin.There's just something about those McDonald's napkins that works wonders on optical glass. However you must have the sanding block to do a good job. Don't try and use other kinds of napkins, as McDonald's has the only good ones for this job. The lens cleaner will get off that baked on cheap glass cleaner residue. When you are done, you will not be able to tell there is glass in the window frame. 
Oh yes, since this topic is in regards to film projection, I am moving it to the Film Handler's Forum.