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Are some stocks more susceptible to scratching than others?


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#1 Oliver Smith

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Posted 05 July 2007 - 06:07 PM

Are some stocks more susceptible to scratching than others?

...and at what stage in their life are they most prone to scratching? When wet? Is undeveloped stock more prone to scratching than processed stock?
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#2 John Sprung

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Posted 05 July 2007 - 07:23 PM

Are some stocks more susceptible to scratching than others?

...and at what stage in their life are they most prone to scratching? When wet? Is undeveloped stock more prone to scratching than processed stock?

I remember in the old days that ECO 7255 was reputed to be more scratch prone than other stocks. Any emulsion is more vulnerable when wet, which should really only be when it's in the developing machine.



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#3 Charles MacDonald

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Posted 05 July 2007 - 08:33 PM

one trick is that the emuslion of undeveloped film can be exposed by "presure" which could turn a minor scratch into a permanent mark, often in colour.

If the film does get scratched before processing, and it is not damaged enough to create a "presure mark" the scratch may "level out" in the processor. (enusion side only) Hence the "technique" of re-washing the film to reduce the effect of scratches.

The REMJET may also save undeveloped film, a very minor scratch on the back that does not go through the rem jet will wash away when the remjet is removed!
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#4 Oliver Smith

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Posted 06 July 2007 - 06:31 AM

one trick is that the emuslion of undeveloped film can be exposed by "presure" which could turn a minor scratch into a permanent mark, often in colour.


I'm not too sure I understand what you mean by "pressure".
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#5 John Pytlak RIP

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Posted 07 July 2007 - 12:24 PM

I'm not too sure I understand what you mean by "pressure".


A burr or rough spot in the gate or on a roller may press on the surface of the film, not enough to actually cause a scratch, but enough to put pressure on the silver halide grains and expose them. Pressure marks are usually in the top (blue sensitive) layer of camera stocks. Faster films tend to be more sensitive to pressure marks, since the silver halide grains are larger and more sensitive.
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#6 John Pytlak RIP

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Posted 07 July 2007 - 12:30 PM

one trick is that the emuslion of undeveloped film can be exposed by "presure" which could turn a minor scratch into a permanent mark, often in colour.

If the film does get scratched before processing, and it is not damaged enough to create a "presure mark" the scratch may "level out" in the processor. (enusion side only) Hence the "technique" of re-washing the film to reduce the effect of scratches.

The REMJET may also save undeveloped film, a very minor scratch on the back that does not go through the rem jet will wash away when the remjet is removed!


Yes, "remjet" often does serve to protect the back side of the film from minor scratches. Rewashing can be very effective in "healing" superficial emulsion-side scratches, as well as in removing embedded emulsion side dirt particles. The Kodak Processing Manual has specifications for a special rewash process "RW-1":

http://www.kodak.com.../h2409_03.shtml

For many years, the term rewashing referred to the common practice of running processed film through a complete process for a second time. This operation removes dirt and/or heals slight emulsion scratches and digs. Rewashing a film once in the original process produces minimal changes in the dye stability and sensitometry. However, several rewashings may cause a change in density over the exposure scale of the film. By omitting the developer and bleach when the film is rewashed, changes in density can be minimized.

Rewash RW-1 is designed to avoid these sensitometric and dye stability changes, and at the same time, to produce similar emulsion swells to that obtained by going through the original developer.
Rewash RW-1 Sequence

Step Function
1. Prebath PB-6 Swells the emulsion, causing the scratches to be filled in and embedded dirt particles to be released.
2. Wash Removes unwanted chemicals, which, if left in, affect dye stability.
3. Final Rinse FR-1 Contains a wetting agent to help prevent water spots while the film is being dried.
4. Dry Dries film for subsequent handling.

The rewash machine consists of a loading elevator, tanks for the prebath, wash, and final rinse solutions, and a dryer. Submerged rollers and rack-drive assemblies will minimize spattering of solutions and aerial oxidation of sulfite in the prebath. Type 316 stainless steel is suitable for tanks, racks, and recirculation equipment. Use 10-micron filters of polypropylene, fiberglass, or bleached cotton in the recirculation system. Use no squeegees, except after the final rinse, where a high efficiency final squeegee is needed.
Mechanical Specifications for Rewash RW-1

Process Steps KODAK Formula Temperature1 Time Replenisher (Wash Rate) per 100 ft. (30.5 m) of
35 mm Film2 Recirculation ®;
Filtration (F)
Tank and Replenisher °C °F min:sec
Prebath PB-6 21 ± 1 70 ± 2 2:00 600 mL R & F
@20 to 40 L/min
Wash -- 21 to 38 70 to100 3:00 300 mL3 None
Final Rinse FR-1 21 to 38 70 to 100 :10 400 mL R & F
@20 to 40 L/min

1 Fahrenheit temperatures are primary. Celsius temperatures are rounded consistent with process-control requirements.

2 For 16 mm film, use one-half the 35 mm film replenishment and wash rates.

3 Use a two-stage countercurrent wash.


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