Ink Jet Printers and the Color Wheel

Ink jet printers operate on a similar principle to lithographic printers, and in turn this can be an application of the lessons learned with the color wheel. With the color wheel students are taught that three primary colors; Red, Blue and Yellow, make up the colors available to the human eye through variation in quantity and balance.
Printer inks are designated C (Cyan) for blue, Y (Yellow) for Yellow and M (Magenta) for Red and K for Black. In lithography and ink jet these four colors are applied to paper as a series of small dots. Of course there is a difference in the way the dots are applied, but a photograph printed in both methods will look similar under a magnifying glass.
Therefore , as on a color wheel, combining yellow and red will give you orange, on an ink jet printer combining yellow and magenta will create orange.

The difference in how this is done is instructive.

To mix orange, using a color wheel and palette, one would place a quantity of yellow paint on the palette and begin mixing in a quantity of red paint until the desired shade of orange is arrived at. Ink jet printers lay down very small dots of ink in varying quantities or numbers of dots. So, for example, to create an orange color the printer will fill a space with yellow (100% Y) and over lay a series of red dots (25% M). The overlay technique works because ink jet inks (and lithographic inks) are transparent; the colors show through from the bottom up.
This would be a good opportunity to bring out a loupe; a small magnifying glass set in an enclosure with a pre-focused distance. If you don’t have a loupe, a strong magnifying glass will work. Have your students identify the dot layout on both a lithographic print and on an ink jet printer. Examples of lithographic prints include magazines, postcards, newspapers, posters, CD inserts, packages and package labels. The students can even estimate the percentage of colors of Black, Cyan, Magenta and Yellow that make up the colors. If you are near any printing houses you might call and request an old set of color separations. These are four clear plastic sheets each one printed in a single color. When all four are overlaid they show a full color photograph but as each sheet is lifted away the contribution of the color is demonstrated.
Adjusting color output in most classroom situations is a matter of guesswork. In professional print houses that employ printers, scanners and computer displays, color calibration is an absolute necessity; the resources required for color calibration are byond most schools.
To use an example of how students can use their understanding of the color wheel to correct color on an ink jet printer, I will use one of my most persistent problems, the tendency of Navy Blue to print purple on my ink jet printer.
From our knowledge of the color wheel we know to combine red and blue for purple. In the ink jet world we deduct that Cyan and Magenta make purple, if our blue looks purple it is because we have too much Magenta in the file. In order to move the print from purple to navy blue you will need to select the graphic in the application and select the CMYK chart. Not all applications allow this, a few have a limited selection of colors you must use. Once the CMYK window is open, simply type in a new, lower, number for M. As I said, this can be a matter of guesswork, i.e. the number for M may not provide the exact shade you are looking for, adjust the number and do test prints until you are satisifed. This method works consistently with all colors, i.e. green too aqua? reduce the Cyan; orange too yellow, reduce Yellow or increase Magenta.

This process will help teach students how to control their printer output as well as reinformce your lessons ont he color wheel concerning primary and secondary colors.

Other useful information:

Photo Cyan and photo Magenta
These are very light shades of blue and red. So, for example, to print pink with only standard Magenta, the dark red dots wold be few and far apart. This can look on on a print. Photo Magenta corrects this by printing many more dots closer together to acheive the same shade of pink. Photo Cyan work the same with light blue.

Piezo and thermal printers
An interesting aspect of the physics of crystals is; if you apply pressure to a crystal it will emit an electric charge, i.e. a spark that will light your stove's burner or a barbeque lighter. The opposite is also true, if you apply a charge to a crystal it will expand. Piezo printers like Canon and Epson use the pressure from expanding crystals to drive the ink onto the paper. Thermal printers like Hewlett-Packard drive the ink onto the paper through heat expansion,

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