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PRACTICAL PHOTO-MICROGRAPHY. 
If there is reluctance on the part of the image to 
appear, and if the high lights appear long before the 
half-tones, and if the high lights become fairly black 
before the shadows appear, or have any strength, we 
may be sure that our exposure has been insufficient. 
With hydrokinone especially, if the image comes up 
somewhat rapidly and soon becomes dense black all 
over, we have over-exposed, but not so much as when 
the image comes up quickly and grey all over. 
Gross under-exposure leads to no image at all, or very 
thin images refusing to take density. Considerable 
under-exposure leads to slowly-developed black and 
white images. Gross over-exposure leads to a flashing 
up of the image, greyness all over, and refusal to take 
density. Slight over-exposure gives generally, but not 
always, very dense images, wanting in contrast between 
light and shadows. 
After proper exposure the image begins to appear at 
the normal time, the high lights first, the half-tones 
closely following, the shadows last ; the processes of 
light and shade development go on gradually, never 
stopping, never rushing; detail is gained first, and 
density gradually follows the detail. 
It is more difficult to describe a perfect negative as 
seen after all the operations have been gone through. 
The background is dense, so that, while the details are 
being impressed in the operation of printing, the ground 
shall remain white. The dark parts of the image are 
fairly dense, yet full of detail, and there is a distinct 
difference between these dark parts (high lights) and the 
