DRAWING REPRODUCTION AND LANTERN SLIDE MAKING H. C. BENEDICTAND R. LEE, CHEMISTRY AND RADIOLOGY D E P A R T ~ NDP TS N O R T ~ S T E UNIVERS~Y RN DENTAL SCHOOL. CHICAGO. I L L ~ O I S
The use of Kodnlith gaper will enable one to make easily, excellent reproductirms of graphs, line drawings, or even tabulated data by direct contact. This paper also can be used to prepare lantern slides of remarkable clarity and contrast.
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When several copies of a drawing or graph are necessary for a thesis or manuscript it is a time-consuming chore to have to reproduce them by hand, and they are seldom all identical. Many lectures or presentations of papers could be greatly improved by tabulating the data or by the use of a graphical method if lantern slides were less expensive or could be made more easily. Resort must be had to photographic methods which are sometimes considered as complicated or unsatisfactory in any but the hands of an expert. The most difficult part of the procedure is to obtain clear-cut black lines on a perfectly white background. Home-made slides of graphs usually havela fogged or blurry background which does not give the contrast necessary for good projection on a screen. ~ " ~ r i n t i npaper g or film which has great contrast is required, and yet none of the usual contrast papers are quite good enough for this purpose in amateur hands. It was suggested that Kodalith, a new Eastman paper which has extreme contrast (in fact it is useless for making positives of "picture" negatives), might he used successfully for our purpose. Kodalith was originated for printers and lithographers for reproduction of pen and ink drawings in which extremes of black and white are necessary. The paper of which Kodalith is made is quite textureless and is used in making either positives or negatives. We have used Kodalith paper in place of film in a film holder, with marked success, in the reproduction of graphs by direct contact, and in the preparation of lantern slides, and felt that others would be interested in this simple method of obtaining excellent results. Contact Reproductions The first attempt made was to prepare negatives of Kodalith directly from a drawing on graph paper. It was found that the paper on which these graphs are printed is not sufficiently textureless to give the best results. So the graphs were drawn on tracing cloth and a negative prepared on Kodalith. These reproductions were to be ordinary manuscript size, 11 X 8.5, and it was found most economical to purchase Kodalith 11 X 14 and cut it to 8.5 inches. The remaining strip was 11 X 5.5 and was used later in making lantern slides. Instead of attempting to center and square the negative paper and tracing cloth exactly, the full size (11 X 14) was 2208
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used in making the negatives and this was then cut to size with the graph placed in the exact position thought best. No printing frame of this size was available, so a box about 10 X 14 X 17 was covered with aflashed opal glass, and a 60-watt bulb was placed in the bottom. The base of the light was ten inches from the top glass and the Inside was painted with aluminum paint. A board around which six thicknesses of blanket were tightly wrapped and fastened was used to hold the paper and tracing cloth in place. The exposure is one second for India ink drawings on tracing cloth, and from 2 to 3 seconds for the positives of negatives so obtained. The exposure should he such that on development the image begins to appear in one-half minute and the development is complete in two minutes. This certainly gives the best results although it has been found possible to vary the time of exposure somewhat and yet obtain excellent negatives. The negatives are developed, using a yellow filter (Wratten Safelight Series 00) which is almost as bright as ordinary light. Of course, for the lantern slides themselves a red Wratten Safelight Series 2 must be used. They are rinsed, fixed, and washed in the usual manner. The developer used was Formula D-85 which is given on the slip of directions accompanying the Kodalith paper. The developer can be used until it takes on a light brown color; after that the developing time is increased and the prints are liable to stain. After the washing it makes the paper slightly more flexible to soak in 10% glycerin solution for a few minutes. The paper will be less curled, if a ferrotype is available for drying. The drying can be markedly speeded up by placing an electric toaster in front of an electric fan and by this combination blowing hot air over the prints on the ferrotype. If the exposure and development have been correct the negative will consist of a dense black background, so dense that a 100-watt lamp will not shine through, and of perfectly clear lines. There is no shading a t all. The negative is now trimmed so that its size is 11 X 8.5 with the drawing or graph in the exact position required. A piece of Kodalith cut to the same size is placed, emulsions together, with the negative and another exposure of from 2 to 3 seconds made. To avoid a thin black margin it is advisable to prepare a border of black paper which can be pasted to the glass and which should be about I/& to inch less than the dimensions of the finished print. This is then treated in exactly the same way as the negative. It is possible t o expose all the necessary positives and then develop them three or four a t a time. When properly done, and the technic is not at all difficult to acquire, the result is a perfect copy of the original drawing with intense black lines on a pure white background, In fact so great is the contrast that slight imperfections, light pencil lines, etc., need not be removed. They do not appear in the final copy.
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Lantern Slide Reparation The extremes of black and white obtained suggested that a lantern slide prepared from it, even using Eastman lantern slides, Slow, would have marked contrast. Such is the case. However, instead of drawing the graph or sketch on lantern slide scale, i t is preferable to make drawings about 11 X 8.5 and reduce them by using a camera. If graphs are drawn in India ink on graph paper, these may be photographed directly; the blue printed coordinates do not show up a t all on the final slide. This is a great advantage, as usually the fine lines are not desired on the slide; however, the important coordinates must be &awn in. If a sketch is made lightly in pencil it may be run over with India ink and photographed on Kodalith paper without removing the pencil marks. Lantern slides of tabulated data can be made excellently and conveniently by photographing typewritten tables made heavily with a new ribbon. In each case a piece of Kodalith paper was cut to fit a film holder and, after focusing the camera, was exposed for a time best determined by experiment. This is almost always required even when using films or plates, so that the lesser cost of Kodalith is another point in its favor. The time of exposure is dependent on the speed of the lens, on the stop used, the reduction in size of the image and the intensity of the illumination. Some examples which we have found successful may be helpfnl. For illumination, a 500-watt lamp in a Kodalight reflector, covered with ordinary tracing cloth to give a diffused light was placed on each side of the camera and about two feet distant from the object. The drawing or typewritten data was held on a drawing board under glass by clamps. The iris diaphragm on the lens was opened and the drawing focused as accurately as possible, and the iris closed somewhat to increase the sharpness of the image. Closing the diaphragm lengthens the exposure necessary but it is frequently worthwhile. I n one instance a half-tone was being converted into a lantern slide. When completed, the screen marks were perfectly clear cut on the slide and were obvious to those sitting near when the image was projected. With the above set-up an 11 X 8.5 drawing cut down to an image of 4.25 X 3.25 (slide size) and a stop of 16, the best exposure was 2.5 minutes, using either a 5 X 8 Tessar l c or 4 X 5 Tessar l l b lens. Doubling or halving this exposure does not particularly spoil the result. A small over-exposure can be compensated by underdevelopment and vice versa but this is not to be recommended for the very best results. For instance, a diagram from the pages of a book was converted t o a lantern slide using the 5 X 8 Tessar l c lens a t stop 8, a 40second exposure required two minutes for development and the result was excellent, a 20-second exposure required two and a half minutes development, and an 80-second exposure required 100 seconds development. The
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last two negatives were quite usable but not as nearly perfect as the first. After treating in the manner previously described the paper negatives can be turned into positives, using Eastman Slow lantern slides. Because of the marked opacity of background the exposure of the plate can be rather widely varied without changing the final product. From one-half to two seconds is about right. The subsequent treatment of the plates is described by the manufacturer in a slip in each package. Lantern slides made in this way have a clear background and dense black lines.
Claims Coal Will Be Basic Fuel for Centuries. Although increasing use is being found for oil and natural gas as fuels, we shall continue to burn more coal than anything else; and when all the oil and gas are exhausted we shall still be burning coal. For after using coal for nearly three centuries the Unitcd States has consumed only one per cent of its supply, and if this country continues to use coal a t the average rate of the past ten years, the known deposits will last about 4000 years. Coal will continue to be the basic fuel because it is cheap, widely distributed, and is abundant, it is claimed in a report made recently before the Amcrican Society of Mechanical Engineers by Henry Kreisinger, combustion engineer of New York City. Mr. Kreisinger declared that prices of oil and natural gas depend largely on the cost of coal. "Coal," he said, "can bc produced a t an avcragc cost of one dollar per net ton. I t can be delivered in large quantities to steam plants a t an avcrage of .83.50 per net ton. Assuming the average heat value of coal to be 12.500 British thermal units as received, the average cost per m.llion B. t. u. a t steam plants is 14 cents." Oil, it was pointed out, has an average heat value of about 18,500 British thermal units per pound. On the basis of heat cost of 14 cents per British thermal unit, a barrel of 336 pounds of fuel oil would cost only 87 cents. On the same basic cost per million British thermal units, natural gas having a heat value of 1000 B. t . u. would sell a t 14 ccnts per 1000 cubic feet, Mr. Kreisinger said. -Science Service Drought Did Not Change Chemistry of Sail. Farmers who believe that last year's drought alTected soil chemically to improve it for this year's crops are mistaken, according to J. B. Kincer of the Weather Bureau. "Abnormal crop growth this year is due entirely to contemporary weather conditions. "he said, "and in no way may be attributed t o improvement of soil conditions." The summer, particularly the month of July, has been unusually warm, and rainfall has been above normal in Atlantic seaboard and southern states, it was explained. Under such conditions, all vegetable matter grows rapidly. The fact that disproves the theory that the soil is chemically changed may be brought out by comparing eastern and southern state crop conditions to those in the corn belt, through the north and northwest. In the corn belt last year's drought was just as severe as in the east, yet subnormal rainfall has caused this year's crops to be below normal. Plenty of heat, coupled with constant moisture due to opportune rainfall, are the causes for abnormal crop growth.-Scieizce Sertke
