PRINTING ON BROMIDE PAPER. 
139 
that of platinotype, and with the permanent bromide 
paper this tone is easily obtained. A paper lately 
introduced by the Kodak Co. bids fair to replace all 
other' papers for our special purpose ; it is called 
“ Nikko.” 
The first requisite is a standard light ; this may take 
the shape of a “regulator” gas burner such as sold by 
Sugg and others, a “standard” candle, a lamp having 
its flame always the same height, or an amyl lamp such 
as is used for certain photometric work. It really does 
not much matter what light is used provided we get 
always the same brilliancy and actinicity. Those 
who have gas at their disposal will do well to use a 
regulator burner ; it is simple, convenient, and suffi¬ 
ciently equable. 
A standard distance is also required: the printing- 
frame holding the negative and the sensitive paper are 
held at the standard distance from the light. Eighteen 
inches will be found a convenient standard of distance, 
but twelve may be taken. It must be remembered that 
the distance must be kept with fair accuracy, because 
the power of the light varies inversely as the square of 
the distance from light to sensitive surface; a small 
mistake in distance may amount to a serious mistake 
in exposure. 
The exposure varies with the density of the negative, 
other things being equal, taking for granted that we in 
each case wish a good black and white. A dense 
negative requires more exposure than a thin one, and 
there is great difference between one negative and 
