Destaining is used to remove a colored stain from a sample. There are many stains performed on prepared microscope slides and other samples that have results that involve a visualization of color. However, sometimes excess stain or a certain color stain needs to be removed so the sample results are clearer or another colored stain can be added.
One of the more common reagents used for decolorization is alcohol. In destaining protocols, it is added for a described amount of time in experiments. Exceeding the required time may completely wash off the stain and give inaccurate results.
An example of how critical time can be in the destaining step is with coomassie blue destaining. Coomassie blue is sometimes used to stain gels in order read results. If the gel is left in the destaining solution for too long, all the blue dye will fade.