Through Tinted Eyeglasses

Looking through red- tinted eyeglasses at a red inscription on white paper, you see nothing but a plain red background. The letters disappear entirely from view, merging with the red background. However, look through the same red-tinted glasses at blue letters an on white paper and the inscription distinctly appears in black, again on a red background. Why black? The explanation is simple. Red glass does not pass blue rays; it is red because it can pass red rays only. Consequently, instead of the blue letters you see the absence of light, or black letters. The effect produced by what are called color anaglyphs, the same as produced by stereoscopic photographs based precisely on this property of tinted glass. The anaglyph is a picture in which the two stereoscopic images for the right and left eye respectively superimposed, the two images colored differently, one in blue and the other in red. The anaglyphs appear as one black but three- dimensional image when viewed through differently tinted glasses. Through the red glass, the right eye sees only the blue image; the one intended for the right eye and sees it in black. Meanwhile the left eye sees through the blue glass only the red image that intended for the left eye, again in black. Each eye sees only one image, the one intended for it. This repeats the stereoscopic and, consequently, the result is the same, the illusion of depth.