Film-Tech Forum ARCHIVE: Shouldn't Opti-Clear White Water glass be NOT green?

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Posted by Frank Angel (Member # 248) on 12-02-2005, 02:10 PM:

I just purchased two panes of glass for my ports that the manufacturer said was "Opti-clear White Water" glass, coated on both sides and with their special hydrophobic coating added which resists dirt and polutants from sticking to the surface. These are 6mm pieces. Yes they are coated and yes when I move them in and out of a bean of light there is change of any kind....either in color or brightness. The coating has all the characteristics of the coating found on lenses -- a bluish shine that you can see if you hold it up to light sideways. Moving the piece back and forth, I see no evidence at all of distortion in the image as I have noticed happens on regular plate glass.

Thing is, althought these pieces in every way seem to be excellent optical quality, I expected their edges to be colorless, or white. They are not. They are GREEN. A green edge to me has always been the sign of ordinary plate glass and unacceptable for projection ports. Is this still the case or is this some kind of new specialty glass? As I said, putting it in front of projected light doesn't at all change the image -- not measurable with a meter or by eyeballing it.

Should I send the stuff back?

Posted by Brian Guckian (Member # 1678) on 12-02-2005, 05:40 PM:

Frank, I've got a pane of optically-coated white water glass, and the cut edge is black. It's not the case I think that it should be clear, as you're looking through the section of the glass.

I'd check with the manufacturer all the same, in case they've given you an ordinary coated sheet of glass; that said, if you can't see any colouration it sounds unlikely that it's the wrong spec.

Posted by Floyd Justin Newton (Member # 1316) on 12-02-2005, 10:53 PM:

Frank--

At the Cine Capri here in Phoenix, we had four 4' x 8' x 1/4"
plates that covered the booth front wall. All were "white
water" and coated. Each cost mucho $$$$$$$$. Paramount Theatres
at the time said that, "We're building a 70mm Roadshow house and
we will not tolerate an inferior picture". That glass had no edge coloring what-so-ever. If I were in your situation I would
demand getting EXACTLY what I was paying for. [Smile]

Posted by Frank Angel (Member # 248) on 12-03-2005, 01:41 PM:

Agreed. I guess my question is, if this may be some new type of glass, because as I said, there is absolutely no change with the glass in or out of the light path and, as far as my eye could tell, no distortion either, as I move in back and forth -- plate glass always makes the image ripple because it's not ground flat on both sides. And there is no question that it is coated on both sides. Bottom line is, if it introduces no apparant ill effects to the image....what's the problem? On the other hand, those green edges have to mean SOMETHINGS not right in Demanrk, eh?

Posted by Steve Guttag (Member # 268) on 12-03-2005, 03:54 PM:

I have seen "water-clear" glass that that once it is coated has a slight green appearence on the edges...I can't explain it but I've seen it. If it does not affect the color temp of the image when you put it in and out then I would not worry about it. There are SO many factors that will affect color temp and the port glass is just one of them.

By your own statements you can't see the difference yet I'll wager that as you make changeovers you can see the color temp difference between the machines.

I also notice the color temp difference in the various reels in a release print...no two are the same.

If you are really curious...obtain a good chromaticity meter and measure the difference.