Scientific American 26, 7.5.1857
Those who are in the habit of writing during evening hours, under artificial light, are aware of the fact that the eyes often suffer from looking upon the white paper. A partial remedy for this evil is the use of light blue colored paper, which is manufactured in great abundance. All our artificial light - that of oil, gas, candles, and any common hydro-carbon - has a yellow tinge, which color excited the retina more than any other in the spectrum. As blue and yellow form a green color when combined - the most agreeable to the eye under bright lights - the benefit of light blue paper to write upon during night hours becomes apparent. The yellow rays of the artificial light strike upon the light blue paper, and mingling with the blue, reflect light green rays to the eyes. All paper, therefore, for writing upon under artificial light, should be of a very light blue color.
The writing paper to be employed by those who have inflamed and tender eyes under bright sunlight, instead of being colored blue, as we have seen recommended in some medical works, should be of a light green color, because the sun's rays are pure white, and such paper will reflect light green rays to the eye from the white solar rays falling upon it. Under no condition, however, should those who have strong and healthy eyes use any kind of paper but white. If writing in a room under bright sunlight they can tone the intensity of the rays with a white screen or other shade, and thus admit subdued white light. There are many persons, however, to whom light green paper would be of great benefit, and as very little writing paper of this color is manufactured - white and blue being the common knds - we would suggest to our paper makers the manufatucre of more light green paper. It should take the place of that dirty yellow colored paper so commonly used in the manufacture of envelopes, &c. Common thick, but well glazed smooth wrapping paper colored green might be economically employed by many persons. All that is required to produce this kind of paper is to mix some blue coloring agent with a proper yellow coloring agent.
The common extract of indigo sold by dealers in chemicals, and a yellow fustic liquor, will color paper a good light green. These two coloring agents, in proper proportions, may be mixed with the paper pulp in the "engine". To insure the action of the indigo, one ounce of the acetate of lead dissolved in warm water should be added when cold, to 1 lb. of indigo, and the solution allowed to stand two or three hours before it is used.
We have no doubt but the foregoing suggestions, if carried our, will be the means of doing much good to a great number of persons.
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