208 PREPARATION OF LANTERN SLIDES ICn. VIII 



323. Smoked glass. For some purposes nothing is better 

 than smoked glass slides. On these one can write or draw with a 

 sharp point either before or during the exhibition. If one takes the 

 precaution to commence writing on the lower edge of the slide and 

 on the face looking toward the condenser the writing or diagram 

 will appear right side up on the screen (see 3 5 for proper position 

 of lantern slides in the holder) . 



Smoked slides must be handled carefully or the surface will be 

 spoiled. 



324. Thin sheets of mica or of gelatin. On a sheet of mica, 

 of gelatin or of non-inflammable cellulose one can write or draw 

 with a pen or brush, using any colored ink. India ink is best for 

 outlines and for written words, letters, or numerals. 



As these sheets are very thin it is best to put a slide made upon 

 one of them between two glasses, so that the sheet will be held flat 

 and be protected. (For other methods of hand-made slides see 

 Dolbcar, pp. 29-32). 



PHOTOGRAPHIC LANTERN SLIDES 



325. Nearly all of the lantern slides now used arc made 

 wholly or in part by photography. 



Negative. First, there is made a negative of the object to be 

 represented in the lantern slide. This negative may be on any 

 size of plate, but the picture should be, if convenient, of the proper 

 size for a lantern slide. That is, its outside dimensions must not 

 exceed 75 x 70 mm. (3 x 2.8 in.). 



This negative should be very sharp and free from defects. Any 

 lack of sharpness or any defects will come out with distressing 

 prominence when the picture is magnified by the lantern. One 

 must then use a good objective in making the picture, or if the 

 objective is not particularly good a very small diaphragm is used. 

 If it is desired that print shall be read easily by all in the room, the 

 lantern slide should not have the letters smaller than six point type 

 (see fig. 216 for sizes of type). 



