This section is from the book "The Fundamentals of Photography", by C. E. K. Mees,. Also available from Amazon: The Fundamentals Of Photography.
The oldest of these development papers is bromide paper. This paper is coated with an emulsion very similar to the ordinary negative emulsions but of somewhat less sensitiveness. The paper is very sensitive to light and must be worked by red or orange light only. The exposure for printing is, of course, very short and the paper is, in fact, mostly used for enlarging, the image of the negative being thrown upon the sensitive bromide paper by a projection lantern so as to obtain an enlarged picture from the negative.
About 1894 Velox paper was introduced and was an entire novelty, since while it was similar to bromide paper in that it is exposed to an artificial light and then developed and fixed, it is so much less sensitive than bromide paper that it can be worked in a room lighted by a weak artificial light and does not require a special darkroom, from which fact it is known as "gaslight" paper. Since the introduction of Velox other gaslight papers have been made and at present almost all prints made by contact from negatives are made on gaslight papers, though Velox is still the best known of all. Velox is about a thousand times slower than bromide paper so that it can be handled safely in any subdued light. It requires an exposure that ranges from about 2 seconds to about a minute and a half, depending on the density of the negative and the grade of Velox used, at one foot from a 25-watt Mazda lamp, and it is characterized especially by the extreme rapidity and ease of its development, from which its name is derived, Contrast and Regular developing fully in 15 to 20 seconds and Special Velox in about 30 seconds. It is consequently possible by using Velox to make prints in comfort and with great rapidity, the old troubles of judging the extent of the printing, and the difficulties with toning baths being entirely absent with this simple and convenient printing medium.
Fig. 76. Degrees of Light Intensities.
Velox paper is made in three grades of contrast to fit different types of negatives. The paper was originally made in the Regular grade only, but it was found that many negatives were too contrasty to print well on this paper and Special Velox was manufactured for use with such negatives, while recently Contrast Velox has been put on the market for use with negatives so lacking in contrast that they will not give good prints even on the Regular grade.
If we make three negatives of the same subject in succession, giving each exactly the same exposure, and then develop these for different lengths of time so that the first will be underdeveloped the second correctly developed, and the third over developed, the first negative will have a short range of contrast, the second a medium range, and the third a long range. If we then print the first negative on Contrast Velox, the second on Regular Velox, and the third on Special Velox, we shall get almost identical prints on all three papers provided that the contrasts of the negatives just fit the various grades of the paper. This is shown in Fig. 77.
Soft Negative of Little Contrast.
Average Negative of Medium Contrast.
Hard Negative of Strong Contrast.
Print from Opposite Negative on Contrast Velox.
Print from Opposite Negative on Regular Velox.
Print from Opposite Negative on Special Velox.
We might think that Contrast Velox would always give more contrasty prints than Regular Velox; it will if both papers are printed from the same negative, but if the Contrast Velox is printed from a flat negative and the Regular Velox from a normal negative, then the Contrast Velox will compensate for the flat negative and give a normal print, just as the Regular Velox gives a normal print from a normal negative, and the Special Velox a normal print from a con-trasty negative.
All the grades of Velox give the same range of reflecting powers in the print provided that they are used with negatives which will enable this range to develop. Suppose we take a black wedge which contains all the degrees of light intensities, from absolute opacity at one end to absolute transparency at the other end and make a print of it. We should get the result shown in Fig. 76. This shows the entire range of reflecting power of which the paper is capable, the range varying from white paper at one end to the blackest silver deposit which the paper can give, at the other.
With any "velvet" surface paper, such as Velvet Velox, we shall find that the white paper will reflect about twenty-five times as much light as the deepest silver deposit. The number of distinct tones which are included in this range from white to black depends, of course, on the ability of the eye to distinguish them. The eye can actually see about one hundred distinct tones in such a range.