Red is widely considered to be the first colour used by early humans, in the form of iron oxide-rich ochres dug from the earth. It is connected with strong emotions and signals danger, an association shared across cultures – around the world, red is the most common colour used for warning and stop signs. Throughout history, artists have used red pigments gleaned from a variety of sources. Modern developments in organic and inorganic chemistry have now seen the red pigment family become one of th

Red eyes: causes, symptoms, diagnosis and treatment