To start platinotype work trusting to chance or good fortune to secure for us good results, means that our whole course will be one of uncertainty and filled with exasperating disappointments to say nothing of the amount of paper and material which is certain to be wasted in unsuccessful efforts.
The reader will probably have learned something of this from his past experiences of negative exposure, the difficulties of which he has by now, we may hope, overcome by careful and patient study, or else if he is not even now undergoing this stage of learning he is the victim of endless mistakes, every plate exposed is a shot in the dark with no certainty attending any one of them.
Exposure, however, in platinotype is not so difficult a matter as that of a dry plate, and the correct exposure with any particular negative once ascertained, every subsequent print from the same negative can, by simple mechanical means, be made with the certainty of its being an exact facsimile of the others.
PRINTING WITH AN ACTINOMETER.
Several kinds of Actinometers are made for sale, the purpose of which is either to indicate the right exposure of a plate in the camera or to tell the duration of exposure for papers such as platinotype or carbon, the image on which is invisible, or nearly so.
A simple, yet thoroughly efficient meter may be made as follows:—Cut some fine tissue paper or papier minéral into strips about a quarter of an inch wide and attach one to a piece of clean glass 4¼ × 3¼ with fresh starch or other colourless mountant. Upon this first strip and exactly over it place a second, but bring it to within a quarter of an inch of the end of the first, next place a third strip in like manner a quarter of an inch short of the second strip, and so on until some seven or eight strips have been fixed. The combination will now be somewhat as the following drawing (Fig. 2), thus forming a tissue band which at each quarter-inch is one thickness more opaque.
Fig. 2.
In the centre of each strip or increased thickness, paint with opaque colour, black or red, a letter or figure as in (Fig. 3). On the back or other side of the glass to which these strips are attached, paint over or cover with opaque paper all except the space covered by the strips. Now place the whole in an ordinary ¼-plate printing frame, with the paper strips inside, next adjust a piece of silver paper, albumenized, or gelatine chloride precisely as though printing from a negative. Close the back and we then have a thoroughly efficient actinometer.