This is topic Prints shedding ... after a few days of bad weather? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Matt Close (Member # 996) on 08-27-2002, 05:56 AM:
I have prints that have been running for a few days with no dramas, then all of a sudden, a few have started to shed quite badly. I was wondering , does humidity affect shedding? I have never seen prints shed this badly, on multiple projectors too, so it isn't a mechanical fault ...... all I can think of is the fact that it has been raining solidly for the last four days now .... 'could' that cause a print to shed?
Posted by John Anastasio (Member # 607) on 08-27-2002, 07:13 AM:
The film emulsion is an organic substance that reacts to humidity. It will absorb water when the absolute humidity level goes up. This will do two things: make the emulsion softer and swell it slightly, both of which will cause increased shedding of the outer layer. I'm sure John Pytlak has some data on the process. I can feel the difference in the film as I thread it when my dehumidier isn't running. The humidity here in New Jersey is frequently only slightly less than that of a submarine with the doors open.
Posted by John Pytlak (Member # 331) on 08-27-2002, 08:19 AM:
Yes, very high humidity makes the gelatin emulsion softer and more likely to build up in the gate. Freshly processed new "green" prints may also have slightly softer gelatin emulsion. Sometimes the heat of the gate causes the gelatin buildup to form hard deposits, that will abrade the surface of the film. Proper print lubrication helps greatly (see SMPTE Recommended Practice RP151). After each show, check and clean the film-contacting surfaces of the gate, and remove any hardened deposits --- a stiff bristled toothbrush is usually sufficient, but your fingernail, a hard wooden "orange stick" used for manicures, or a plastic guitar pick work well to scrape off the really hard deposits. Do NOT use metal or other hard materials that may gouge or nick the gate rails or leave a burr. Some projectionists apply a thin coating of a hard wax (carnauba or paraffin) to the film-contacting surfaces after cleaning.The recommended relative humidity for projection rooms is 50% to 60% RH. If the humidity exceeds 65%, use a dehumidifier. In addition to softening the gelatin emulsion, very high humidity is bad for equipment (rust and corrosion) and electronics (high voltage arcing, corrosion of contacts).
http://www.kodak.com/US/en/motion/support/technical/storage1.shtml
http://www.kodak.com/US/en/motion/support/technical/hand.shtml
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Randy Stankey (Member # 64) on 08-27-2002, 12:24 PM:
Those little, plastic scrapers that you can sometimes get from the state lottery, used for scratching off instant lottery tickets work really well too! 