The Optical Magic Lantern Journal (January 1902)

124 The Optical Magic Lantern Journal and Photographic Enlarger. a sufficient exposure to give the necessary detail in the shadows, as such parts as are represented by bare glass will in the slide be sufficiently opaque to be simply black on the screen. Then, development must not have been so pushed as to make any of the lights, except the very highest, so opaque as to exclude all of the light employed in printing. In other words, no part of the negative should be completely opaque, except the very highest of high light, and of that, as we said, there is little or none in nature. The most suitable negative is one that is rather on the thin side, full of delicate detail and gradation; the negative, in fact, that will give the most technically perfect print on the modern gelatino-chloride paper. The knowledge and the negative having been acquired, the next step is to decide as to the developer that is to be employed; as in slidemaking, the exposure should be made to suit the developer, not the reverse. Just what the developer should be is of less importance than that it should be a fixed quantity, nor is there any particular reducer or formula that can be said to be better than any or than all others. All we can say is that the following has with us and with many others answered the purpose admirably :— Ortol .. ies ae a 160 grains. Potaasium metabisulphite 80 BR Potassium bromide ‘ied ve 40 ay Sodium sulphite os . 2} ounces. Sodium carbonate .. se oe 13) C4, Water to make os 2 .. 10 ” This will make a stock solution, each dram of which contains two grains of ortol, and which, added to seven drams of water, makes our usual developer. From the foregoing it will be evident that correct exposure is the keynote to success in slide making, and that no effort should be spared to secure it. A writer in The Camera Club (English) journal, who is a first-class slide maker, said that he was satisfied if he got one good slide from a dozen plates, but we hardly care to be so extravagant, and therefore, to ascertain just what the right exposure should be under any particular circumstances, conditions of light, plate and negative, we expose one plate in strips, not cutting it, but in a printing frame roughly adapted to the purpose, a piece of ferrotype plate in which is a slit 3 inches by 4 inch being made to slide across the plate to be tested ; and making five exposures, two above and two below what we may guess to be about right. On development, or rather during its course, it is easy to see which of the five is nearest to what is required, and equally so to arrive at what will be absolutely correct. Ona correctly exposed plate the deepest shadows will first appear, and be followed in their order of intensity up to all but the highest lights, and notwithstanding the fact that the deposit is cumulative, none of the shadows except the deepest, if there should be such, will be quite opaque before the necessary detail is developed. In other words, if the plate has received a correct exposure and the development has been arrested at the proper time, there will be no clear or bare glass except on the highest high lights and no shadows so dense as not to transmit some of the projecting luminant, except the very deepest of deep shadows, neither of which are found to any great extent in nature, and both of which should be as rarely and as sparingly found in the slides. Next in importance to correct exposure is the extent to which development is carried. An unwarranted fear of fog induces most slide makers to stop too soon; to stop while most of | the lower tones are stil) bare glass, instead of going on till the shadows have the necessary deposit ; and it is all the greater folly to do so, not only because a trace of fog not unfrequently makes all the difference between a good and a bad slide, but should development be found to have been carried too far, it is easy to bring it back to tolerably correct gradation by one or other of the well-known methods of reduction —Farmer’s, which attacks both the weak and strong parts alike, or the ammonium persulphate, which deals mainly with the denser parts. But, in spite of care both in exposure and development, it may be that on drying the slide is not just as it should be. The shadows may be all right in their gradation, but what should be merely lights more or less translucent are only bare glass, making what should be a sunny landscape appear on the screen as if covered with snow. In most cases this may be mide into a good slide in the following way :—Place the slide and a plate into the printing frame, using the slide as if it were a negative, and expose for a short time to the light. The exposure will depend on the amount of deposit desired, and should be such as when developed and fixed will leave sufficient to give the necessary lowering of the lights when the plate is used as a cover glass. So far, in dealing with exposure, the reicrence has been to “ printing by contact,” the result of which, notwithstanding what has been said to the contrary, is in every respect as good as that from copying in the camera. Butas the former method is applicable only where the negative is of a suitable size, or where only a suitable part of a larger negative is wanted, the latter niust