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This topic comprises 2 pages: 1 2
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Topic: 70mm filmwinds on platter
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 03-20-2005 05:39 PM
quote: Brad Miller (same point also made by Steve Guttag)
Anyone handling a 70mm print had damn well better be far better than simply knowing which way to thread the film so the mag tracks are up against the heads was always the way I looked at it.
Yes - you would hope that only professionals would ever get to handle 70mm. I was just suggesting that the convention identified by Monte came about as an extra safety net. The same applies to full-gate silent prints: you'd hope that only properly trained projectionists would ever show them, but I've lost count of the number of times I've sat in the theatre and seen the opening titles come up in mirror writing.
quote: Stephen Furley
The negatives which I had returned to me from a lab a few years ago were wound emulsion out; in response to a question from myself somebody replied that negatives are always stored this way.
That's not what the SMPTE or FIAF recommend, at least for nitrate and acetates. I'll look up the relevant standards and quote the chapter and verse if you like (and if John P doesn't beat me to it!). I frequently get preservation elements back from labs emulsion out, too, and have to reverse them before they go into the vault. I think this is simply the way they came out of the drying machine rather than anything deliberate.
quote: Stephen Furley
I'm sorry, but I don't follow this either. I do find that particularly with polyester prints I sometimes need to look quite closly to see which is the emulsion side, but it would be difficult to mistake which side of a print the mag stripes are on, surely.
Difficult, but not impossible, especially if the print is being handled by someone who isn't used to running mag. And all human beings can make mistakes. As I said, I'm only suggesting that this is a convention, not a technical necessity.
Incidentally, I seem to remember someone telling me that mag-striping the emulsion side of acetate elements required the use of a chemical which was so environmentally incorrect that the EU banned it years ago and the mere mention of its name is enough to give the Swampy brigade multiple heart attacks. I don't know how true this is, though.
quote: Stephen Furley
In the 'French' section of MOMI the picture was direct rear projected, i.e. no mirror. Was a special reversed print made for this, or was it a special projector, with the sound head on the opposite edge?
It's been 13 years since I worked there, and I'm afraid I really can't remember. Those compilations were all specially made prints anyway (thanks to those horrid endless loop platters, the prints only lasted for a couple of months each), and there were several other BP installations in there - the screen above the mock Odeon frontage, for example.
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 03-21-2005 09:47 AM
quote: Leo Enticknap
Incidentally, I seem to remember someone telling me that mag-striping the emulsion side of acetate elements required the use of a chemical which was so environmentally incorrect that the EU banned it years ago and the mere mention of its name is enough to give the Swampy brigade multiple heart attacks. I don't know how true this is, though.
The solvents used in the binders for magnetic striping formulations can be handled properly, but meeting environmental regulations can be costly, especially for low volume film striping operations as opposed to making magnetic tape. Even magnetic tape manufacturers like Quantegy have struggled:
Quantegy Article About Magnetic Tape Manufacturing Process
quote:
Analogue tape consists of three primary components: the base film, the magnetic coating and the back coating. The Mylar (polyester) base film is shipped to the plant on industry standard 660mm (28-inch) wide rolls. The coatings are manufactured on site from a variety of different ingredients depending on the application. The magnetic coating, for example, includes the magnetic oxide, binder, lubricants, whetting agent and solvent, and so on. For analogue tape there can be as many as 26 ingredients. Quantegy actually produces 57 different tape products using 16 basic formulae.
Contrary to popular belief few tape manufacturers actually produce their own magnetic particles. These are normally bought in from specialist suppliers.
The mixing of the ingredients is done in the Mix-Prep building. A critical part of the process is to ensure that the magnetic particles are evenly distributed throughout the binder. Another important consideration is to avoid breaking the magnetic particles as this generates non-magnetic particles, which reduces the sensitivity of the tape or creating clumps of particles, which increases distortion. Milling is the first stage of the process and this is done in large diameter drums containing either glass beads, steel balls or even stone pebbles. This can take up to 72 hours for an analogue tape. Video formulations tend to take less time as the magnetic particles are needle shaped and are therefore more easily damaged. The magnetic coating for video is also produced in individual batches whereas audio tape is treated differently.
Having the consistency of flour, the magnetic particles once mixed with the other ingredients, is stored as a slurry ready to be pumped to the coating area. For audio, typically 400 gallons of mix will be produced at a time and this 400-gallon mix is then added to a 1,500-gallon blend tank. This ensures that any variation, no matter how slight, is offset by the much larger quantity of mix already in the blend tank. This is important for consistency. It takes about a gallon of mix to produce a 2,500ft reel of 2-inch tape...
Once the mix has been applied, the magnetic domains in the coating need to be aligned. This is done by passing the through a strong magnetic field that aligns the North and South poles of the magnetic particles down the length of the jumbo tape. Once this has been done the coating is dried by running the tape through a series of large ovens that vary in temperature from 150°F to 100°F. The length of these drying lines, and the speed at which the freshly coated tape travels, varies according to the product (audio or video) being made. Oven lengths vary between 200ft-500ft and the tape travels between 200ft-800ft per minute.
What is remarkable is that throughout the drying process the tape does not touch anything, but is suspended on a cushion of air as it travels the length of the oven.
Once dried the surface of the magnetic coating is calendered. This is done by passing the tape between two rollers, one made from stainless steel and with a mirror like finish, and the other made of paper or plastic with a measured amount of give in it. This literally irons the surface of the tape forcing the binder that has risen to the surface during the drying process back into the magnetic coating and imparting the characteristic gloss like finish to the recording side of the tape...
Back in Opelika, a lot of the work done by the Chemistry Lab is concerned with quality control, both of incoming materials and during the manufacturing process itself. The staff is also involved in research work as well. One of the key responsibilities is to ensure that the correct amount of catalyst is being added to the magnetic coating. With as many as 10 different mixes being use on a shift this has to be constantly checked. Another important criteria is the mix viscosity. This has to be carefully monitored and it is also critical that the mix ingredients are probably dispersed. All these things are constantly being checked.
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