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Subject: Liquid gate printing

Liquid gate printing

From: Doug Nishimura <dwnpph>
Date: Saturday, June 8, 1991
Got your notes.  I was talking to Barbara [Brown] about her response to
the liquid gate printing.... Anyway, she said on the phone that you had
suggested that perhaps the answer should not be too literal, but more a
general thought on the idea of printing through liquids.  Too late.  The
mail to you had already gone that afternoon.  I had taken it a little
less literally than Barbara, but more so than you did.  I had assumed
that he meant to try printing through liquids in a frame similarly
designed to a liquid gate printer. I perhaps should add that one
addendum to my blurb about liquid gate printing.  It is a rather long
section from an abstract by Joseph W. Schmit from Technicolor, Inc.,
Hollywood, California.  The paper is entitled "Optical Printing
Techniques", Proceedings, Two-Day Tutorial Seminar: Technologies in the
Laboratory Handling of Motion Picture and Other Long Films, ed. by Frank
P. Clark, 159-178, Society of Motion Picture and Television Engineers
and the Society of Photographic Scientists and Engineers, 1971.

    ------------------------------------------- "Wet Printing

         In optical printing from color negative, it is usually
    (although not always) desirable to use specular illumination to
    obtain the best possible image.  This has a disadvantage, however,
    in that scratches and other surface blemishes on the negative show
    up very prominently in the product.  The scattering effect of a
    scratch due to the difference in refractive index of air and film is
    shown in the drawing.  If one fills the scratch with a material that
    has the same refractive index as the film, then the scratch will not
    show.  One way of accomplishing this is to lacquer the film.  This
    has some limitations.  The lacquer, in drying, may take on the
    configuration of the scratch, although it will not be so pronounced.
    Lacquer also is subject to chipping and scratching and is therefore
    not a permanent solution.

         A practical solution is to coat the negative with a liquid with
    the correct refractive index, print through the liquid then strip it
    off, leaving the negative in its original condition.  Such a system
    has been in use commercially in the motion picture field since 1957,
    and many laboratories with optical printing facilities now have some
    form of wet printing capability. An added benefit of this "wet
    printing" is that one gets more printing through in the high lights
    [sic] because of the reduced scattering from the surface of the

         There are several methods of applying the liquid varying from
    quite simple to quite complex.  In one method the negative is run
    through a tank where it picks up the liquid, then is passed through
    an air doctor which controls [sic] the amount of liquid remaining.
    The air flow to this air doctor can be varied to accommodate
    different printer speeds. Vacuum can be applied to the perforation
    area.  The negative is seated wet in the printing aperture, then is
    taken up through a blow-off type dry box.  Another "open face"
    method applies the liquid from a pad, another from spray jets, and
    another from a roller to coat just one side.

         A different approach is the "liquid gate" type.  The negative
    runs through the printing gate between two glass plates.  The liquid
    is introduced under pressure to the space between the plates and
    removed by vacuum.  The film is vacuum cleaned going into the
    movement and vacuum squeegeed going out.

         Yet another approach is to completely submerge the printer
    movement in a tank of the liquid with glass ports in the optical
    path, or to place the printer movement just above the liquid with a
    separate printing gate in the liquid.

         Which type of wet printing is used depends on the nature of the
    film to be handled and the type of printing equipment available.
    All methods are adaptable to a range of speeds, although the open
    face cannot be used at extremely low speeds (below 4 ft/min.) or
    hold frame, and the submerged movement can usually not run quite as
    fast as the others.  All can be adapted to run in either direction.

         The open face method requires no change in the printer
    movement, but the printing aperture plate has the seating surface
    eliminated or reduced to a thin line at the bottom and/or top in the
    picture area. Since no change is made in the movement, film pitch is
    no problem.  If it will run above the minimum speed, it will run
    wet.  In fact it will probably run better wet than dry because of
    the lubricating effect on the negative.  This method suffers when
    [a] hard-to-wet negative is involved, such as when the negative has
    undergone some post development surface treatment.  Occasionally
    there may be edge effects, also splices tend to carry a bead of
    liquid with them increasing the apparent width by as much as 100% in
    the print.  In some instances, depending on the printing format,
    this will be objectionable on the screen.

         The liquid gate method requires more modification of the
    movement, although does not eliminate its use for dry printing.
    With highly specular illumination, and with some types of printing
    where the depth of focus is large, dirt or spots on the outside
    glass surfaces may become a problem, and when used dry there is also
    the risk of scratching the windows.

         The submerged movement cannot be used dry because of the
    difference in actual distance and optical distance from the film
    plane to copy lens.  The optical effect of the mixing of a liquid
    with varying composition or temperature must be avoided in this
    method of printing.

         Several different liquids have been used commercially and many
    others have been tested.  The one most commonly used is
    perchloroethylene.  Its vapor is relatively non-toxic [!!!], but
    must be controlled.  It is non-flammable and has a reasonable cost.
    Extensive testing before the initial commercial use and 13 years of
    use have shown that it does not adversely effect [sic] negative film
    or its silver or dye image.  The refractive index of
    perchloroethylene, 1.504, is midway between that of triacetate film
    base and the gelatin over coating on the emulsion side.

         It is practicable to apply the liquid on a once through basis,
    except in the liquid gate or spray applicator, or in a recirculating
    system.  In any case, the liquid must be supplied to the negative
    without suspended dirt or soluble contaminants which may harm film.
    Water content must be kept to a minimum (cloud point below + 5 C)/
    The liquid should be at room temperature or slightly above,
    depending on which system is used, to avoid the condensation of
    water from the air as the solvent evaporates.

         Wet printing has been attempted in continuous contact printing
    also, but its main use is in optical printing...."

I left out the footnotes and diagrams.

I'm sure that'll hear lots of chatter on the net about AIC.  Hope I
didn't miss anything super-duper by not being there.


                   Conservation DistList Instance 5:4
                   Distributed: Sunday, June 9, 1991
                        Message Id: cdl-5-4-005
Received on Saturday, 8 June, 1991

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