A great many photographers think of panchromatic plates only as a means of photographing difficult subjects where it is desirable to secure a correct rendering of various colors in monochrome. Panchromatic plates are equally useful in securing an incorrect rendering of certain colors when the result in monochrome is more satisfactory, but in any case color filters are necessary. It is not possible to make a panchromatic plate that is not more sensitive to blues than to other colors, so this correction must be made with a filter when the negative is made.

There are two kinds of color filters, orthochromatic filters and contrast filters. The orthochromatic filters of the Wratten series are designated as K.l, K.2 and K.3. The K.l gives a slight color correction, K. 2 considerably more, and K.3 correct rendering of all colors in proportion to their relative brightness.

The proportionate correction is determined by the amount of blue light these filters absorb, and as the plates are very much more sensitive to blue than to other colors, the entire surplus of blue light must be absorbed to give absolutely correct rendering. This necessitates a considerable increase in exposure so that the lighter K.l and K.2 filters are used where absolute correction is not necessary, and the darker K.3 filter only for correct rendering.

Filters of a greater depth of color are known as contrast filters and will make certain colors appear lighter or darker, such incorrect rendering often being desirable in commercial photography. This has been illustrated in copying prints yellowed with age or stained.

The yellow portions photograph as black with an ordinary plate. With a K. 3 filter and panchromatic plate the yellow markings photograph exactly as they look, but with a dark G. filter the yellow photographs as white and the resulting negative is as clean as though a fresh print had been copied.

The same use may be made of the green and red filters, especially the deep red which causes red objects to photograph as white, provided they are not too dark or the red does not contain black, as is often the case in some forms of printing or lithographing. Letters or documents containing notations or stamps in red ink, however, can be photographed with the deep red filter without any indication of the red ink marks showing in the negative.

The special use we have in mind for a panchromatic plate and contrast filter is for reproducing valuable negatives that have become so badly stained that they are useless for printing.

Negatives become stained in various ways and sometimes these stains cannot be removed by chemical treatment without injuring the silver image. It is useless to try to print from them, but it is a very simple matter to reproduce them, provided the chemical that made the stain has not removed a portion of the silver image, and this is not often the case.

A positive made through the strong Wratten G. filter on a panchromatic plate will show no trace of the yellow stain. It is then a simple matter to make a negative on a Seed 23 plate from the positive, by contact, if the positive is of the desired size.

Using one of the regular Wratten filters will necessitate making the positive in the camera, but contact positives of stained negatives may be made by using a piece of gelatine filter film large enough to cover the entire negative.

The film is not expensive (10c per square inch, about), but care should be used in handling it. It is stained gelatine, stripped from the glass support on which it was coated, and without a support it must be kept absolutely dry to retain its form.

One does not have stained negatives to contend with every day, but there are very few studios in which a valuable negative is not at some time unavoidably marked for life. Whether it is a red, a green or a yellow stain, the red or green or yellow filter will miraculously cause it to vanish as the positive is made on the panchromatic plate.

It must be a panchromatic plate, however, for its sensitiveness to red and green and yellow is the secret of the many seemingly miraculous things that may be accomplished with Wratten Plates and Filters.

Many other advantages in the use of Wratten Plates and Filters are explained in the booklet "Color Plates and Filters for Commercial Photography" which we will be glad to mail you free on request.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt New York.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt New York.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt New York.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt New York.