Chromatography is a technique used to separate mixtures of compounds. In both thin layer chromatography (TLC) and paper chromatography a spot of pigment is put onto a chromatography plate or paper. The lower end of the plate or paper is put into a solvent. The solvent creeps up the paper (by capillary action) and slowly moves past the spotted mixture of pigments. Each pigment dissolves in the solvent or clings to the paper to different degrees. After a period of time the different pigments in the mixture end up spread out between the original spot and the upper most point reached by the solvent (called the solvent front).