Paper chromatography
Paper chromatography is an analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...

 technique for separating and identifying mixtures that are or can be colored, especially pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s. This can also be used in secondary or primary colors in ink experiments. This method has been largely replaced by thin layer chromatography
Thin layer chromatography
Thin layer chromatography is a chromatography technique used to separate mixtures. Thin layer chromatography is performed on a sheet of glass, plastic, or aluminum foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose...

, however it is still a powerful teaching tool. Two-way paper chromatography, also called two-dimensional chromatography
Two-dimensional chromatography
Two-dimensional chromatography is a type of chromatographic technique in which the injected sample is separated by passing through two different separation stages. This is done by injecting the eluent from the first column onto a second column...

, involves using two solvents and rotating the paper 90° in between.