This section is from the "Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1911" book, by Aristo Motto. Also see Amazon: Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1911.
This unusual diverting of the negative image to that of a positive or a combination of the two in which the positive image overshadows that of the negative, has been encountered as far back as 1860.
The explanation given is that the partially developed image acted as a negative, and the underlying bromide of silver, with the latter action of light, receives a positive impression, as in a printing process.
With continued development this becomes stronger than the negative image and causes partial or almost complete reversal.
Our Trouble Department occasionally hears from a photographer who, when developing his plates, has been mystified by getting positives instead of negatives.
This reversal may be produced in different ways, but the most frequent cause is the secondary action of light on plate after development has begun.
It may be due to light entering dark room or on account of the developing light being actinic. Other causes are prolonged over-exposure or the presence of Hypo in the developer.
The latter causes, however, are comparatively infrequent and for this reason they will not be considered in the present article. Explanations given by some of our representatives to the effect that reversal is due to fog during the process of development, are not always accepted as being correct and we, therefore, decided to make some experiments showing conclusively how reversal can be produced at will.
No. 1 shows print from negative having normal exposure and normal development.
No. 2 shows slight reversal of the photographic image. This effect was produced by carrying the developing operation until same was about three-fourths completed, then giving an exposure of about one second to an actinic light, returning negative to the developer and completing development. The plate shows a slight reversal of the deepest shadows and is an effect which proves most puzzling to the average photographer.
No. 3 shows further reversal. This plate was left in the developer until development was about one-half completed, then exposed to the light for about one second. In this case the negative character begins to noticeably disappear. The reversal of shadows is complete and the reversed action of the light begins to extend to the half tones.
In No. 4 a still further reversal is seen. This plate was exposed to the light for one and one-half seconds after being only one-fourth developed. Development was then completed. In this plate the reversal of the deep shadows and half tones is practically complete. Only the high lights retain the negative values in the plate.
No. 5 shows almost complete reversal. This negative was one-fourth developed, then exposed to the light for two seconds and returned to the developer for the normal period of development. The result is an almost perfect positive. Only the most extreme high lights retain negative values in the plate.
In these experiments Seed 26 X plates were used and the same exposure in camera was given for each plate. The plates were all developed for the same length of time and the same kind of developer was used for each. Similar experiments with other brands of plates gave the same results.
From An Artura Iris Print By Dudley Hoyt New York City.
In the minds of many photographers this has been held a "freak" result, due to unexplain-able causes. As a matter of fact it is a simple experiment that can be made by anyone for his own satisfaction. The amount of the reversal is controlled by the relation between the time of development before and after exposure to actinic light. The shorter the preliminary development - after a well defined image is formed - before this secondary action of light takes place, and the longer the subsequent development, the greater the reversal.
Reversal of the photographic image is natural and simple, given the necessary conditions. The moral is: For perfect negatives be sure that dark room light is safe, and use a plate tank.
This is a practical dark room lamp for the professional that is strong, sensibly constructed and mechanically correct as to ventilation. It is simple and easy to clean, the front glasses fit into light tight grooves, the ruby glass being double thickness and bound with a metal frame which has a lifting ring. The orange glass fits in front of the ruby and may be removed at will. The side lights are of heavy ruby glass and the front is protected by a hinged cover, supported at any angle by a metal rod. The lamp may be used with either oil or electricity, and when oil is used, the height of the flame may be controlled without opening the lamp.
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