Chromatography of Inks


Chromatography of Mr. Sketch Pen Colors

Light and color make our surroundings more pleasing and stimulating. Color selection in paintings, theater lighting and commercial displays are three applications where lighting is very important.


Application of three colored light sources, red, blue and green, on a white background illustrates the additive properties of light. When a red and a green light are super-imposed on the same area, the color observed is yellow. The diagram on the left may be used to predict the color seen when these three primary additive colors combine. Variation of the intensity of each source produces different shades of color. (What additive primary colors would you select to produce a white light?)


A second approach to color production is use of a white light with filters to subtract specific colors from the white light. This process is illustrated on the left above. Cyan, yellow and magenta filters can filter out red, green and blue to produce various colors. Color variations can be adjusted by the amount of each dye in an ink.


A white light source with a cyan filter results in a cyan colored image. Combinations of filters absorb light to produce other desired colors. White light with a magenta filter results in a magenta colored spot (can also be produced by radiation with red and blue light sources). A magenta light source with a yellow filter results in a red color. The diagram below illustrates this subtraction of light with a white light source and a yellow filter. Note that the blue light is absorbed and removed by the dye. The same color could be produced with red and green additive primaries as light sources.

Two filters in succession, cyan and yellow with a white light source produce green. After the light passes through the cyan filter, the first filter, the light is cyan. The two primary colors that remain are red and green. The chart below may be used to predict the color with a combination of one or two filters.


What color would an ink be that is made of a mixture of cyan and magenta dyes? What color primary subtractive dyes would you select to produce a black image?


This diagram illustrates the separation of a black ink formed from the three dyes cyan, yellow and magenta. Water is the solvent. What would you expect to observe if you were to separate a green ink? A red ink?