Film-Tech Forum ARCHIVE: Emulsion Fogging

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Posted by Robert John Jeromson (Member # 2559) on 11-16-2004, 05:23 PM:

Can anybody explain what causes the emulsion fogging on certain prints, I have had to replace numerous reels in the past that have this discolouration (some worse than others) but haven't been able to find a suitable explanation.

Rob.

Posted by Darryl Spicer (Member # 711) on 11-16-2004, 07:13 PM:

Probably cause by the safe light used in the dark room when splicing raw stock together was to close to the raw stock or to bright causing the fogging.

Posted by John Pytlak (Member # 331) on 11-17-2004, 08:32 AM:

Here is a presentation on Darkroom Illumination that I gave at an SMPTE Technical Conference:

http://www.kodak.com/US/en/motion/support/illumination/page01.blind

Posted by Frank Angel (Member # 248) on 11-17-2004, 08:56 AM:

Just what kind of fogging? It would be great if you could snap a pic to post. Of course all of what John and Darryl have said is true, but to honest, Robert, in all the years I have been in a booth, I have seen print fogging that is caused by errors in the darkroom only once or twice, whereas you seem in imply that it is a common occurrance. If you are finding this on prints coming directly from the lab, i.e., first run, then, yes, it may be lab errors, but I have to say that given the frequency that you seem to imply, I would have to wonder what the boys in the lab are smoking, because I think it would be quite unusual to find this kind of problem except very rarely. But if you are seeing it on prints that have already been in circulation, then I would think that possibly the emulsion could have been damaged by other theatres up-stream of you.

Emulsion can be "stressed" by excessive heat. In its early stages, this results in a kind of "embossing" of the emulsion and a slight discoloration of the surface. Exposure to higher temps can cause the emulsion to "bake," giving it a distinctive brown discoloration. After that, even higher temps will cause it to blister and then actually burn through.

Perhaps you are seeing the very early stages of heat damage. This is, of course, pedicated on the theory that you are getting these prints after other bookings.

Posted by John Pytlak (Member # 331) on 11-17-2004, 01:02 PM:

On a color print, heat damage will usually take the form of "embossing" (a physical deformation of each frame related to the localized intensity of the radiant energy). Extreme "hot spotting" may cause a breakdown within the emulsion layers, causing kind of a "snowflake" pattern in darker areas of the picture, and an opalescent spot on each frame visible by reflected light (magenta-blue when viewed from the emulsion side, and yellow-green when viewed from the base side). In some cases, the repeated exposure to extreme heat caused the dyes to migrate, causing a colored halo around dark objects in the scene. I recall seeing lots of magenta dye migration with non-Kodak prints of "The Fugitive", "The Magic Garden", and "Free Willy".

Always check to be sure lamp alignment is correct, heat filters are still effective, and that you are not "hot spotting" the light:

Heat Damage 1

Heat Damage 2

Posted by Robert John Jeromson (Member # 2559) on 11-17-2004, 01:31 PM:

Thanks for your help guys. Frank, sorry, just to clarify, it is a rare thing I have had only two this year, one in I Robot which was new direct from Atlab in Australia and one in Spy Kids 3-D which was used ex US.