The following table will give an idea of the percentage of light reflected from ordinary wall-hangings and papers:
Per Cent. Reflection | ||
White blotting-paper | .82 | |
White cartridge-paper | .80 | |
Ordinary foolscap | .70 | |
Ordinary newspaper | .50 to .70 | |
Chrome yellow paper | .62 | |
Orange paper | .50 | |
Yellow wall-paper | .40 | |
Yellow painted wall (clean) | .40 | |
Tracing cloth, pale blue | .35 | |
Light pink paper | .36 | |
Blue paper | .25 | |
Emerald green | .18 | |
Dark brown paper | .13 | |
Vermilion paper | .12 | |
Blue green paper | .12 | |
Cobalt blue paper | .12 | |
Black paper | 0.5 | |
Deep chocolate paper | 0.4 | |
French ultramarine blue paper | 3.5 | |
Black cloth | 1.2 | |
Black velvet | 0.4 |
151. It is very difficult to select practical artificial illuminants, because of the various color properties possessed by each. A Welsbach mantle, which gives a greenish tint, is pretty sure to alter the character of any color other than green. Incandescent electric light, as well as ordinary gaslight, contains a yellow tint.