SCIOPTICON MANUAL. 65 



ty, and as free as possible from all defects. As the 

 magic lantern slide is generally 3J x 3J, it is not desir- 

 able to employ a very large negative. 6 x 8 will 

 answer the purpose better tban a larger size. But neg- 

 atives upon smaller glass will be found to give even finer 

 results. On the other hand, it is very bad policy to 

 attempt to enlarge a positive to double or treble the 

 size of the original negative. The negative should not 

 be smaller than the positive. 



The Lens. Any good portrait combination, of six to 

 eight inches focus, quarter-inch stop, will work to ad- 

 vantage. Lenses of very short focus and very small 

 opening, are not recommended. 



The Development Should be conducted with great 

 care and judgment, as it is the most important part of 

 the whole process. Rather underexpose and underde- 

 velop, and as soon as the detail is visible, flood the plate 

 with water, and check further action. Avoid an excess 

 of light during development, and dread the appearance 

 of the slightest fogging as the worst enemy to be en- 

 countered. 



Fixing Solution. Cyanide of potassium, after which 

 wash well in running water. 



Toning. It is frequently of benefit to the positive that 

 it should be toned, and at the same time slightly strength- 

 ened, to give contrast to the picture when projected upon 

 the screen by a powerful light. Many chemical solutions 

 may be used to accomplish this purpose. A weak solu- 

 tion of gold gives good results; also, a dilute solution of 

 bichloride of palladium can be recommended. In either 

 case the solution is flowed over the plate, after fixing. 

 The positive is then dried and varnished. 



The Finished Picture Should be free from the slight- 

 est appearance of fog; the high-lights, the sky in land- 



