What is shadow masking?

Shadow masking is a technique used in the manufacture of color cathode ray tube (CRT) displays. It involves placing a mask between the electron gun and the screen in order to block certain colors of light from reaching the screen. This creates the patterns of red, green, and blue sub-pixels that combine to form a full-color image. Shadow masks are typically made of metal and are precision-crafted to exacting specifications in order to ensure that the sub-pixels are defined sharply and with great accuracy. This technique was widely used in CRT displays until the rise of LCD technology, which does not require shadow masking.