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    Autochrome - Printing from Plate - Making Tri-color Filters - Wratten Equivalents

    To prepare permanent prints from screen-plate pictures,
    one must have recourse to one of the tri-color
    subtractive methods already described; to utilize these
    it is obvious that we must have the three constituent
    negatives, but these are not difficult to make. The first
    requisite is a set of sharp-cutting filters, the purpose of
    which is to isolate each individual color, that is all the
    red, all the green, and all the blue. These filters must
    be of such a nature that they transmit only the light
    of one color. They can be made without much trouble
    and as they are not used except as light screens, they
    need not be made with such careful attention to parallelism
    of surfaces, or cementing, as is necessary in the
    case of lens filters. It will in fact be more convenient
    to make them the full size of the pictures.
    The red filter can be made from two glasses, one coated
    with methyl violet and the other with rose Bengal and
    tartrazin, or crystal violet and tartrazin. The rose Bengal
    filter is made from:
    Tartrazin 10 g
    Rose Bengal 5 g
    Gelatine, 8 per cent solution 700 ccm
    The methyl violet is:
    Methyl violet 0.7 g
    Gelatine solution 700 ccm
    The crystal violet is:
    Crystal violet 0.4 g
    Tartrazin 5.0 g
    Gelatine solution 700 ccm

    The above quantities are sufficient for i square meter.
    It is not advisable to mix the violet with the rose Bengal.
    A few drops of glacial acetic acid may be used with both
    the violets to facilitate solution. Unless the dyes are used
    in the form of a solution previously made, care must
    be exercised that they are actually in solution. There
    should be no difficulty in this, as they are readily soluble
    in the hot gelatine, only, if added all at once, small
    lumps of the dyes may become coated on the outside
    with chilled gelatine and may therefore not dissolve
    well. It is preferable to make the gelatine solution
    double strength, use half of the water to dissolve the
    dyes, and then mix. The dyed gelatine should be filtered
    through linen that has been well washed and wrung
    out of hot water.
    The green filter must be made with two glasses; one
    should be coated with:
    Tartrazin 2 g
    Naphthol green 1 g
    Gelatine, 8 per cent solution 700 ccm
    and the other is coated with:
    Acid green JE 0.5 g
    Gelatine solution 700 ccm
    In place of the acid green, 3.0 g of brilliant green may
    be used.
    The blue filter is prepared with:
    Yellowish eosin 4.0 g
    Gelatine, 8 per cent solution 700 ccm
    3.0 g bluish eosin may be used instead of the yellowish.
    The second glass is coated with:
    Methylene blue 4B 1g
    Gelatine solution 700 ccm

  2. #2
    Mustafa Umut Sarac's Avatar
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    For those who do not want the trouble of making the
    niters, the Wratten & Wainwright gelatine film filters of
    the requisite size may be bound up between glasses. The
    numbers of their filters are, for the red No. 29 or F,
    for the green No. 61 or N, and for the blue No. 50 or L.

    A moment's consideration will show us that as we
    want to reproduce the red, we must use a red-sensitive
    plate, and it will be found more satisfactory to use panchromatic
    plates for all three negatives, as by doing
    so the gradation in the three negatives will be more
    alike than when we use different kinds. There is some
    latitude here, as we are able to modify the final result,
    and one might choose a panchromatic for the red, an
    isochromatic for the green and an ordinary plate for the
    blue filter exposures; but it cannot be advised. Whether
    a fast or slow panchromatic plate be used is of no particular
    moment; the slow kind will give as good results
    as the fast and is less likely to fog. At the same time
    it must be borne in mind that we are making negatives,
    not transparencies, and this must be kept in view in
    developing. Brilliant-looking plates with clear glass
    shadows are not the desideratum; but soft negatives,
    rather thin in the high-lights, with fully exposed shadows,
    should be aimed at. It is immaterial what developer is
    used, and the beginner should use that to which he is
    accustomed. Naturally the desensitizing process may
    be adopted, and the plates should be backed.
    In the reproduction of a screen-plate it is clear that
    we might place it with the film in contact with the sensitive
    plate. Then we should have the color elements
    reproduced quite sharp, and every negative would be
    broken up into minute dots corresponding in size. For
    some positive processes this might not be a disadvantage,
    but in the case of the separate system in which the positive
    is bound up with a viewing screen, we cannot obtain
    contact with the sensitive surface. The result will
    be more or less want of sharpness, but this will not be
    of serious moment, and it breaks up the screen pattern,
    so that almost closed or continuous tone negatives are
    obtained. Actually it is advisable to follow the same
    plan with an autochrome, that is, to interpose between
    the sensitive surface and the picture film a colorless
    transparent medium of greater or lesser thickness.
    There are some very simple mathematical formulas
    by which we can tell not only what ought to be the thickness
    of the intervening medium, but also the distance
    of the light source, and the resulting want of sharpness
    in the resulting negatives. But one of the main ideas
    in this little book has been to avoid, as far as consistent
    with clarity, mathematics and deep theory, so that it
    will be assumed that it is required to make the negatives
    from autochrome and Paget pictures.

    https://archive.org/details/practicalcolorph00walliala

    PRACTICAL COLOR
    PHOTOGRAPHY
    BY
    E. J. WALL, F.C.S., F.R.P.S.
    Author of
    "The Dictionary of Photography,"
    " Carbon Printing," etc.
    SOUTHERN
    AMERICAN PHOTOGRAPHIC PUBLISHING CO.
    BOSTON 17, MASSACHUSETTS
    1922

    COPYRIGHT, 1922, BY
    AMERICAN PHOTOGRAPHIC
    PUBLISHING CO.
    Entered at Stationers' Hall
    PRINTED IN THE UNITED STATES OF AMERICA
    Electrotyped and printed, June, 1922
    THE PLIMPTON PRESS
    NORWOOD, MASS. U.S.A.



 

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