Palatography is a technique used to identify which parts of the mouth are used when making different sounds. This technique is often used by linguists doing field work on little-known natural languages. It involves painting a coloring agent, such as a dye or a mixture of charcoal and olive oil on the tongue or the roof of a person's mouth and having that person pronounce a specific letter or sound. A photograph is then made of the mouth roof and tongue in order to determine how the sound was articulated. The technique can also be performed electronically using a tool called a pseudo-palate, which consists of a retainer-like plate lined with electrods that is placed on the roof of the mouth while the speaker pronounces a sound. A record made through palatography is called a palatogram.