LANTERN SLIDES. 
157 
into the bottle whence it came ; it is important to have 
the varnish filtered after each time of use, for any dust 
on a slide appears as a large blemish on the screen. 
When the varnish has dried, a short time at ordinary 
temperature, the slide is ready to be “ mounted.” 
The mounting of a slide is for its preservation, and 
the process consists of laying on the film a “ mask ” of 
opaque paper, having a suitable aperture cut out of 
it; laying over the mask a sheet of glass three-and-a- 
quarter inches square ; and binding the edges of the 
glass plates with adhesive paper “strips.” It is very 
convenient to have the masks black on one side and 
white on the other; in mounting, the white side is laid 
uppermost, and the title of the subject written on it, 
with any other particulars desired. It is also well to 
have masks with various sizes of apertures ; frequently 
we do not wish to show as much subject as occupies a 
three-inch circle. Wormald’s masks and strips are 
worthy of recommendation. If it is of importance to 
show the image on the screen with a particular margin 
upwards, the mounted slide is laid down on the table 
as it is wished to appear on the screen, and two small 
marks are put on the cover-glass at the two top corners 
of the slide ; this is a standard mark for the lanternist. 
In the lantern the two marks go into the carrier next 
the light and downwards. 
Mention might have been made of other processes 
for slide-production, as wet collodion, which is almost 
unapproachable for the purpose; albumen, and dry 
collodion. Other developers might also have been 
