How does red glass make objects look red?

Answer: Red glass only transmits red

Glass adds red color to light — Wrong. Glass doesn't add color. Red glass absorbs most wavelengths except red, which it transmits. Objects appear red because only red light passes through.

Red glass only transmits red ✓ — Correct! Colored filters work by selective absorption. Red glass absorbs blue, green, and other wavelengths, transmitting primarily red (~620-700nm). When you look through it, only red light reaches your eyes from objects. Red objects stay red, but blue objects appear black (no blue light transmitted). It's subtractive color filtering!

Red wavelengths amplify — Wrong. Wavelengths don't amplify. Red glass selectively blocks non-red wavelengths through absorption, allowing only red light to pass through.