What is blues cups?

Blues cups are a type of cup used in blues music performances. They are also known as "harmonica cups" because they are often used with the harmonica. The cup is held against the player's face, creating a natural amplifier and distortion effect. Blues cups can be made of metal, plastic, or glass, and may have various sizes and shapes. They have been widely used by blues harmonica players since the 1920s and continue to be a popular accessory in the genre.