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As long as the tension on the film is reasonable, the "twisting" normally encountered on a platter system should not cause any permanent film deformation. SMPTE Recommended Practice RP 106 specifies "Film Tension in 35-mm Motion-Picture Systems" as needing to be less than 16 ounces.

When you do see uneven winding or "spoking", it is often due to excessive curl of the film. Film consists of a thin (about 0.0006 inches) gelatin emulsion coated on a thicker (about 0.0047 inches) polyester support. The gelatin emulsion adsorbs or loses moisture quickly, and shrinks as it dries out. The polyester support is very dimensionally stable with changes in humidity. At very low humidity, the emulsion shrinks enough to cause the film to cup in toward the emulsion, known as "positive curl". At very high humidity as the emulsion adsorbs water and expands, the film may curl slightly in the other direction, known as "negative curl". Note that this effect was less with triacetate base, because the triacetate base changes dimensions with humidity more than the very stable polyester base does. Processed print film will usually lie flat at about 50-60 percent relative humidity, which is why Kodak specifies this range for optimum film handling.

Under very dry conditions, excessive curl may cause uneven winding or spoking. Winding tension also affects this. Changing humidity, winding orientation or tension usually helps.

One possible risk of twisting film under tension is the possibility of peeling apart a splice. Typical cement or ultrasonic splices are very strong with a straight pull of tension, but may peel apart from the edge if the film is twisted under tension or twists against a roller flange.

BTW, Kodak does test film on platters, as well as reel-to-reel. Our lab has both Strong and Cinema Film Systems platters, and we have a Christie on order.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

Do you guys ever intentionally increase the takeup tension and overly twist the film when you thread it...just to see?

I do know of one theater that had SPECO platters (the new design with 3 elevator rollers on top...which of course, don't take up with much tension) and he added weights to the elevator rollers to increase the tension. Personally, I think it was way too much, as getting the center ring out was a challenge, but his film never broke or had any damage.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

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We do have a new Christie P35GP. So far, it has shown more film abrasion and dusting than similar older Christie projectors at a local Hoyts theatre, where we have done extensive testing. This is not uncommon, as running lots of film usually smooths out film contacting surfaces, so a projector usually shows less abrasion as it "wears in". The latest version of Kodak Vision print film looked very good on the Christie projectors at the Hoyts theatre, and had less abrasion than any other polyester film we tested, even on more abrasive projectors.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

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Might want to forget about that print now. It's been far too long and the depot would've either sent it back out or inspected it...taking away from the pristine condition you could've received it in. If only I could've UPS'd it direct to you!

I'm sure Toy Story 2 will play for a few months. Come visit!

All projectors contact the area of the print between the perfs and along the edges. The usual source of any abrasion is the projector gate/trap/bands and the intermittent shoe. The amount of abrasion depends upon the design of these components, the materials used, the surface finish, the tension against the film, and whether the surfaces are clean and free of nicks, rough spots, or hard deposits.

Abrasion of the perf and edge areas was rarely a problem in the past, since nothing was printed there. Over ten years ago, when digital sound on film was first being developed, Kodak deliberately put its Cinema Digital Sound (CDS) track in the area of the analog soundtrack, to avoid the risk of projector abrasion degrading soundtrack life. Although Dolby Digital and Sony SDDS tracks have excellent redundancy and error correction, projector abrasion between the perfs and along the edges can increase error rates and compromise the useful life of the digital tracks.

Severe abrasion of polyester film base is also known to cause more "flaking", "shedding", or "dusting" of the film base than triacetate film. The reason is the difference in the way triacetate and polyester base are manufactured. Triacetate is made with the plastic material dissolved in solvent, and "cast" onto a heated coating wheel to evaporate the solvent and leave a plastic film. Although it can be abraded, triacetate's amorphous nature minimizes "flaking". Polyester base is melted and extruded, and then "stretched and tentered" to orient the plastic molecules to give it its strength. But the oriented molecules allow the surface of the base to delaminate or flake when subjected to severe abrasion. Back-side coatings help resist abrasion, but add to the dusting if the abrasion is severe enough to "break through" the coatings.

The emulsion side of the film can also be abraded. Since it is made of gelatin which readily adsorbs moisture, the hardness of the emulsion is greatly affected by how the print was dried after processing ("green prints" tend to be more easily abraded or cause buildup), and the relative humidity. Prints used in very damp or tropical environments may show more emulsion abrasion and buildup in the projector. Kodak recommends keeping the relative humidity between 50 and 60 percent RH, and never over 70 percent RH. If the projector gate is too hot to touch, consider a water-cooled gate to reduce buildup of hardened emulsion.

Proper film lubrication greatly reduces abrasion of the film by the projector, much as wax helps protect the finish of furniture or an automobile from abrasion. Although the film manufacturers do put lubricant in the raw stock film, the amount that they can add is limited. Too much lube will cause rolls of film to be too slippery, and can cause winding and tranport problems in film laboratories and theatres. Some of the lube is removed during processing.

For optimum projection performance, film should be lubricated after processing. This has been documented in numerous published reports dating back to the early 1920's. Kodak's processing manual (H-24.02, H-24.09) and SMPTE Recommended Practice RP 151 specify that 35mm prints should be edgewaxed for optimum projection life. Unfortunately, few labs edgewax prints anymore, because of the environmental restrictions on the solvents used to dissolve the wax. Kodak is evaluating other possible solvent-free lubricants (e.g., silicone, emulsified wax, solid wax, etc.), and proprietary post-process film treatments (e.g., FilmGuard, TomaKote) that act as film lubricants. We have found that a very small amount of S.C.Johnson Paste Wax (carnauba and paraffin wax) applied to the side of the film roll can act as an "emergency lubricant" by depositing wax along the edge and between the perfs, but do not recommend this as a routine method.

In general, projectors that use non-metallic materials in contact with the film rarely have abrasion problems. Some labs actually project valuable negatives and master positives using "velvet gates". Film-contacting components made with engineering plastics like Delrin can significantly reduce abrasion, but these softer materials can wear faster, and need to be replaced on a regular schedule. We have found that projectors "out of the box" often produce more abrasion than projectors that have run lots of film --- running millions of feet of film burnishes the metal components that can abrade the film. (One way of doing this faster is to run full-coat 35mm magnetic sound recording film, as the oxide coating acts as a fine "emery cloth"). Always check alignment and finish of new projector components, to be sure there are no "rough edges". Our well-used Century projectors produce almost no abrasion.

Use the minimum gate/shoe tension needed to get a steady image. Film contacting components should be kept clean and free of nicks or rough spots. Use a hard bristle toothbrush, fingernails, and plastic tools to remove any buildup. Never use metal tools or abrasives (steel wool) to remove deposits, as you may cause a burr or nick. Some projectionists apply a fine coating of hard wax or other lubricant on the film-contacting parts before threading.

Kodak continues to work with projector manufacturers to optimize the choice of materials, design, and finish to reduce projector abrasion. We are working to develop new methods of print lubrication. Significant improvements have been made to the films themselves, and continue to be made.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

Oh Brad, this is an easy one.
Ballentyne Pro35, The projector wears out before the print does. With its plastic film gate and trap and its fiber main drive sprocket it is guaranteed to break before the film wears out.

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Just as with the paste wax idea, the trick is applying the right amount. Too little doesn't penetrate to the perfs, where it is needed. Too much penetrates into the image area, where it may show up on the screen if it isn't spread evenly.

We have already observed the "streaking which resembles vertical lines of water on the projected image" you mention when FilmGuard is applied to the film for the first time. I suspect that the uneven application that would result from just applying it to the side of the roll would be quite visible. But we'll try it anyway.

We've already tried the same idea with silicone oil and silicone spray. Applying inert silicone oil the side of the film roll was almost impossible to control without getting "oily mottle". The silicone spray (silicone dissolved in a fast-evaporating solvent) worked well for some customers when it was carefully applied using a pad damp with the spray. (Never spray anything directly on the film, as it is almost impossible to control the level of application). The silicone spray deposit on the edge was barely visible and significantly reduced projector abrasion.

Another thing to be careful of is the slipperiness of the roll. Rolls that are too slippery may not wind evenly, or tend to dish or cone out. I would worry about someone trying to carry a large roll(e.g., transferring to another platter) without support. Likewise, lots of lube may make the roll more prone to slip on the platter surface.

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John Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Research Labs, Building 69, Room 7419
Eastman Kodak Company
Rochester, NY 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243

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