Can Crystals Show Color Mixing?

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Author: Michael Calhoun
Physical Science  
Grade Level

Elementary (grades 2 through 4)  

Difficulty of Project

$12.00 excluding the cost of the Tri-fold cardboard display board 

Safety Issues

Investigator should not ingest the crystals or drink the liquids associated with the activity. The crystals used in the project are extremely slippery when spilled. Never flush or pour these crystals down the drain, crystal swelling could possibly clog drainpipes. Also handling food dyes can stain both hands and clothing it is advisable that the young investigator wear gloves and an apron. 

The supervising adult should discuss the warnings and safety information with the child or children before commencing the activity. 

Material Availability

The materials required for this project are readily available and inexpensive. 

Approximate Time Required to Complete the Project

Two hours 


Hydrogel superabsorbent polymer crystals are able to soak up as much as 500 times their weight in water! The research aspect of this science fair project is to determine if these crystals will absorb food dye and when the different colored crystals are placed in contact with each other, will the colors mix by the process of diffusion.

This science fair project focuses on a special kind of polymer called a hydrogel superabsorbent crystal which absorbs water, swelling to many times its original size. This water absorption ability will be used to determine if these crystals can be used to show color mixing by the process of diffusion. The investigator will place hydrogel crystals containing different colored dyes into a slender tube or bottle and observe if there are changes in color as the dyes mix via the process of diffusion. From the observations made a data table will be generated based on the results of the investigation.

Materials and Equipment / Ingredients

Hydrogel superabsorbent crystals, plastic cups, food coloring, Sieve, 4 to 8 sections of a plastic fluorescent tube casing, or tall-slender empty plastic container, disposable gloves, and an apron.

With the possible exception of the crystals, all the other items can be purchased from the local supermarket, hardware, homebuilding or garden supply store. Also, a Tri-fold cardboard display board can be purchased from an art & crafts supply store.

The hydrogel crystals can be purchased either locally from a garden supply store or online from the following venders: Science in A Bag, Educational Innovations, or Nasco Science


A hydrogel crystal (sometimes called a “Disappearing crystal,” “Water Crystal,” “Superabsorbent gel,” etc) is a long chain of molecules bonded together to form a superabsorbent polymer, that does not dissolve, but forms a gel when placed in water and is often used in garden, landscape, and farming applications as a way of retaining moisture. Instead of dissolving, these crystals absorb water, swelling to many times their original size. The crystal is made up almost entirely of water. As they dry, water is slowly released to the soil. Some of these crystals can soak up as much as 500 times their weight in water! This superabsorbent characteristic makes hydrogel crystals useful because they can absorb water in which food coloring has been added and when place next to each other the colors will mix as the coloring seeps or diffuses out of the crystals. 

Diffusion is the process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration. 

As the young investigator will discover layering blue, yellow, and red will produce orange and green which will seem to appear out of nowhere! If the investigator obtains the three primary colors of blue, red, and yellow he/she can mix any shades of color listed on the color wheel.          


Food coloring purchased from the grocery stores typically comes in the three colors of blue, red, yellow along with green. By definition, the primary colors are the main colors that the investigator can combine in some prescribed amounts to arrive at any other color. 

To achieve other colors, check out the tips written on the food coloring package label. Mixing equal parts of any two primary colors produces the secondary colors of green, orange, and violet. For example, one drop of red mixed with one drop of yellow will create orange; one drop yellow plus one drop of blue makes green; and one drop blue plus one drop of red makes violet.

Digital photos can be taken during the experimenting process and/or images of hydrogel crystals can be downloaded from the Science in a Bag website for free and without copyright infringement issues. Images of a color wheel to place on the Tri-fold cardboard display board can be downloaded from the Internet. 

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