While great care has been bestowed on the original selection of the colors of all these above-described papers and every effort is constantly exercised to keep them the same from year to year, the subject is materially complicated by the guarantee required of the manufacturers that no arsenic colors shall be used in the preparation of any of the papers. This guarantee is strictly insisted on, because, while the writer has never been able to learn of any authentic case where a child has been injured by the use of plated or glazed papers, he believes that the opinions of parents and teachers should be respected in the matter, although the arsenic colors are often the most permanent and the aniline substitutes which are necessarily used belong to a class which is the most fugitive of all colors.
The line of colored papers now in use is the result of many experiments on the part of the writer and careful tests by experienced teachers for several years, and in its present condition affords but small indication of the time and care which has been expended on it. This has been inevitable, because the peculiar system on which the colors are based has been one of growth and the papers have been designed to afford the necessary material colors for this special scheme of instruction.
In preparing the tints and shades in the papers many experiments have been made to determine the true effect of light and shadow on each normal color, and then to imitate these effects in the papers.
All this is independent of the professional tricks which artists use to heighten their effects, some of which are legitimate, while others may be questionable on sound principles.
It is a common habit with artists to introduce very warm effects into all sunlight by the use of orange or yellow in the warm colors. This extreme tendency has been intentionally avoided in the preparation of these papers, however desirable or allowable it may be considered in heightening effects. So also in the shades as in the tints, the aim has been to keep all the tones of one color in the same scale, even though artists
