This section is from the "Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1913" book, by Aristo Motto. Also see Amazon: Studio Light Incorporating The Aristo Eagle - The Artura Bulletin 1913.
There is an immutable law of cause and effect in the exposure and development of a plate, on which depends the quality of the negative. To be sure there is a certain flexibility to this law, but this is regulated entirely by the amount of latitude or flexibility of the plate emulsion.
Avoid under-exposure in negative making. To the same degree you under-expose, will your negative fall short in its scale of gradation. You can't develop detail in shadows that have never had an exposure, and you can't secure a full scale of gradation in a negative until you get into those shadows with the required amount of light.
Of course, the first thing one thinks about when underexposure is encountered, is more exposure. That is logical enough, but there are often other and better remedies than longer time of exposure. I stepped into a studio the other day where I feel sure about twenty-five per cent. more light could have been secured by the judicious use of soap and water on the skylight and curtains covering it.
Take a look at your lens, if you have not cleaned it recently, and see how much more light would reach your plate if that haze were removed. A lens gathers moisture and the moisture gathers dust, and in a short time there is a hazy film over its surface which effectually cuts down the amount of light entering the camera.
Then there is the fast Seed "R" Plate or the equally fast Eastman Portrait Film, both of which combine speed with those very essential qualities, - latitude and gradation. If you are using a slow plate you can get more exposure without an increase of time, by using a fast plate. But regardless of how you arrive at the result, get the necessary amount of exposure.
In equally clear weather, exposures will need to be about four times as great in December as in June. And this is the month of December.
You may be exposing correctly, you may be under-exposing and don't know it, but if you are, your results will show it. Many a good "workman has fallen into the habit of making exposures a little short of what they ought to be without realizing it. It's a very simple mistake and one easily fallen into.
From An Artura Iris Print By O. C. Conkling St. Louis, Mo.
Practice makes it possible for you to make a number of exposures almost identical in time. In September you gave exposures of three seconds under certain conditions. In October and November you do the same thing, and the falling off in quality from the under-exposure is so gradual that you hardly notice it unless you go back and make a comparison with your full timed negatives.
It is barely possible that you have fallen into this habit of under-exposing. Make several negatives of various exposures and see how much time is really necessary to over-expose. And see if the full timed negatives don't pick up a lot of quality when printed.
It's better to be on the over than on the under side of correct exposure.