Staining
Staining is what happens when color from a drink or food soaks into a surface and stays.
When you spill grape juice on a white cloth, the juice soaks into the fibers and leaves a colored patch. The color bonds to the material and stays even after the juice dries. Scientists do the same thing to cells and tissue samples. They add a colored dye that soaks in and sticks to certain parts, making those parts visible under a microscope.
Explaining staining by grade level
When you drink dark drinks, some color stays on your teeth. The color sinks in and will not rinse off with just water. Some stains go deep, and some sit on top. That is why some drinks leave worse marks than others.
Projects that explore staining
Color from a liquid soaks into a surface and stays, that is staining. In this experiment, 60 tiles are soaked in five common staining liquids for two days. Then five cleaners go head-to-head: store-bought toothpastes versus homemade formulas built from baking soda and water. Each tile gets exactly 25 brush strokes with one quarter teaspoon of product.
When color from a drink soaks into enamel and stays, that is staining. Five teeth are cleaned to the same starting color, then each is soaked in a different beverage, coffee, tea, grape juice, red wine, or cola, for three minutes. After removing the teeth, the stains are compared and ranked from darkest to lightest.