The Optical Magic Lantern Journal (March 1902)

The Optical Magic Lantern Journal and Photographic Enlarger. 145. Wet Collodion Lantern Slide Making.—No. IV. By ALFRED H. SAUNDERS. Cf pA HIS article, which concludes the % series, deals with a few causes of failure, and replies to some letters of general interest. One correspondent writes :-—‘‘ [I have followed out instructions in articles and tried to copy some prints, but find the negatives very thin and lacking in vigour. What is the cause, and how can I remedy it?” It is possible that under-exposure in camera may be the reason. Collodion plates require much longer exposure than dry plates; try longer exposure and a slight excess of acid in developer. If this does not answer, try redeveloping, and for this purpose make up the following :— No. 1. Pyrogallic acid. . : 10 gre. Citric acid a 25 ers. Distilled water. . 2 ozs. No. 2. Nitrate of silver oe ia Pes 20 grs. Distilled water.. ae 2 ozs. For use mix 4 drachm of each, and after washing plate, pour on and off into measure glass till sufficient density is obtained; or an alternative intensifier, which gives a rich chocolate colour to negative, is prepared with :— Iodine 60 gre. Water 6 ozs. The negative, after being fixed and washed, is immersed in this until it attains a lemon colour throughout. After washing, place it in bath made with :— Sulphite potassium Water .. ea 6 grs. 6 ozs. or into the stock toning bath described in third article, when it will rapidly gain in density ; after which well wash, dry, and varnish. Various Markings on the Finished Slide.— These are evidently caused by altering the position of plate when taking it from bath previous to placing it in dark slide. The remedy is obvious. Put the plate in slide in the same position you take it from the bath, and the silver solution will not run down as this has done. Lines across the Film are caused by hesitation when immersing plate in bath. I have received, which I think are | Lines in Direction of the Dip are caused by allowing the film to get too dry before immersing in bath. Silver Stains on Film.—These are caused by | scum that has accumulated on top of solution in bath. A piece of blotting paper drawn across top of solution or filtering the bath will remedy this. Pinholes.—You say you well wiped out | camera and dark slide with a damp cloth, so that dust is not the cause in this case. Have you put too much iodide into bath? This will sometimes prove a source of annoyance, and the only remedy is to dilute bath with water and make up to strength with silver again. Filtering the bath sometimes helps. Image very Thin in Centre of Slide.—From the appearance of this slide there is evidently a reflected light somewhere, either in the camera, whose sides are perhaps not dead black, or the camera points to a window. Change the angle, and reblack the camera inside, when the glare | spot should disappear. Bradford.—Your query is too large an order for both the space in the Journal and my : leisure. / endeavoured to keep clear of all technical While writing these articles I have terms, and to make them simple and easy to follow. You can get the complete chemical history and process of the baths, etc., from A Manual of Photography, by J. F. Hardwich get if possible the 1861 edition), Captain Abney’s Practice of Photography (before 1880 edition), or the British Journal of Photography ' Almanacs for 1874 to 1877 contain articles by : the late J. Traill Taylor, all of which will give you help and information. Dry Plate Camera.—Decidedly not! If you value your future negatives you will not use this for the work. A modern camera, unless specially made, is useless for collodion work. You might get a special back and dark slide made to fit it, but this will cost more than a second-hand studio camera of the old school. Medico ‘Teacher, York. — Line drawings, diagrams, and subject matter for class teaching. You will certainly get better results with collodion, both for negatives and slides. The lens I can recommend from practical experience for the work you want to dois a 4-plate ‘‘ Cooke,” Series III. It is about the most perfect lens you can get tocopy written matter, line diagrams, ete. The definition it gives and the resulting slides are superb. Any dealer will get it for you, or the makers will send you all particulars if you write them.