341. It will be seen that in all the preceding instructions in this lesson, the utmost diligent must be excercised in securing the entire absence of white - light during the preparation of the plates and their manipulation. Light may be admitted in any quantity, but it must be of a quality of color that is harmless. This may be arranged by pasting ruby - colored may be detached in the following manner: Grasp the rod just above the emulsion with the thumb end forefinger of the left hand, and with the right hand twist the rod round, at the same time pulling upwards. The emulsion will thus be readily forced off the rod. Now take it (the emulsion) between the fingers and thumbs of both hands, press out of it as much alcohol as possible, rinse it with a little fresh alcohol, and the operation will now be completed. In case it is desired to keep the consolidated emulsion for any length of time, it should be put at once into a bottle in order that it may keep moist, because after it has once been allowed to become quite dry there seems to be considerable difficulty in redissolving it. When required for use, with a clean pair of scissors cut up the cake of emulsion into thin slices, letting these fall as they are cut into a beaker filled with cold water, in which they must be allowed to remain an hour (or longer if convenient), after which pour off the water, fill up with fresh, let stand for a short time, and then drain off this also. Now place the beaker in water heated to about 130°. Let it stand in this for ten minutes, then add as much rater as may be required to make up the quantity to three ounces, stir well, filter, and the emulsion will be ready to coat the plates. It is quite essential that plates prepared with emulsion made as above directed should be developed with ferrous oxalate, as they are very subject to green fog when the alkaline developer is used. As regards exposure, I find that at two feet from an ordinary No. 8 gas - burner the time required is about three seconds. Though I consider these plates better adapted to printing than to anything else, still they will be found by no means bad for any purpose where great speed is not required, and where the oxalate development is admissible. - H. Houlgrave.
841. After a series of experiments I came to the conclusion that, if two non - actinic media were placed in close contact, there would be a less perfect light filtration (if I may so term it) than if the planes or intercepting surfaces of (say) the glass or paper were separated by a small intervening space. It seems to act almost like a " double filtration," the actinic rays being neutralized far more effectually than if the same media were placed in immediate contact Another simple wrinkle which no one should miss is "to grind one side of your ruby or orange glass." This softens or mellows the light and prevents any direct flare from the flame reaching the plate. When developing, I have found this a sure cure for light fog, when caused by the lantern. If you want to improve the illumination, after grinding the surface of the glass rub over the ground side a little grease. A little emery or pumice powder rubbed on the glass will soon obtain a ground or mat surface. My next hint on lanterns will, I think, be rather novel in character. It is nothing more nor less than, instead of using glass or paper for the non-actinic medium, to adopt a "colored" liquid to pass the light through. This has the following advantages: You can weaken or strengthen it to any depth of tint; also, any thickness or volume of colored medium can be used to meet the requirements of your sensitive plates. Non-actinic glass cannot be met with except of a thin kind, but by my method you can have density from one - eighth of an inch upwards. With this power available, the chance of fogged plates from unsuitable "light" vanishes. This principle can be easily applied to any form of lantern, as the cell containing the colored paper over the glass of the dark-room, or by the use of a lamp or lantern protected properly by ruby-colored glass or paper.
342. A few words as to the apparatus needed for this interesting process for work outside, and then it must be left to grow, and grow as it surely will, into public favor. In the Lesson B, the camera-box is described, so that here allusion need only be made to the double holders and the changing - box, either of which may be used to suit the inclinations of the operator. Of the latter first. The annexed diagram represents what is known as " the old-fashioned dryplate changing - box." It is often used instead of the double holders. The liquid is simply adapted for the lantern in the form of a slide, grooves being provided to receive the slide; and this answers also in place of a hinged door. I find the illumination of two sides of the lantern suficient, and this I place angle-wise in front of me when at work. A small hinged hood of tin will be found useful for protecting the eyes and keeping the light on its work. This is, of course, fastened to the top of the slide, and when in use acts like a sloping awning over the illuminated surface of glass, and ought to be fixed to all lanterns, as it effectually prevents any upward rays of light. To make the slide, get two pieces of clear glass of equal size, and about one and a half inches larger than the lighting surface of your proposed lantern. Get some strips of glass or wood, about three-eighths of an inch wide, and of any thickness you may require your fluid chamber. I use three-eighths of an inch. Now take the strips of glass and cement them round three sides of one sheet and along the fourth side; also cement a strip, but leaving an opening of half or three quarters of an inch. When all is set firm, with a brush lay cement over the strips so fastened, and then press the remaining sheet of glass on the top of the same. This completes a glass box, as it were, a hole being left at one corner edge between the sheets of glass for pouring in the liquid. When all is again set, work a little marine glue round the edges, and then bed the whole in a rebated wooden frame, still leaving the corner hole. This forms your glass screen complete. If the lantern grooves are made wide enough to receive two screens, you can fill one with orange and the other with ruby solution, and can use them either separately or together, or neither. When non-actinic light is not required, simply drop the slide into the lamp grooves in the same manner as when inserting the slide in the back of the camera. - W. Clement Williams.