Black is a color created by the complete absence or absorption of visible light. It is an achromatic color, without a tint like white and gray. It is often used symbolically or figuratively to represent darkness. Black and white were often used to describe opposites such as good versus evil, the dark ages versus enlightenment, and night versus day. Black has been the symbolic color of solemnity and authority since the Middle Ages and is therefore still often worn today by judges and magistrates. Black was one of the first colors used by artists in Neolithic cave paintings. It was used as the color of the underworld in ancient Egypt and Greece. It became the color of mourning in the Roman Empire and over the centuries has often been associated with death, evil, witches and magic. In the 14th century it was worn by kings, clergy, judges and government officials across much of Europe. It became the color worn by English romantic poets, businessmen and statesmen in the 19th century and a couture color in the 20th century. According to surveys in Europe and North America, it is the color most commonly associated with mourning, end, mystery, magic, strength, violence, fear, evil and elegance. Black is the most used ink color for printing books, newspapers and documents because it offers the greatest contrast against white paper and is therefore the easiest to read. Similarly, black text on a white screen is the most common format used on computer screens. As of September 2019, MIT engineers are making the darkest material from vertically aligned carbon nanotubes.