Non-polar solvents are of little use in staining, and are more commonly used to ensure that the staining process stops completely. Ionic reactions largely cease under such conditions and the preparations are, to all intents and purposes, permanent. The simplest solvent is water, and it is undoubtedly the most used. Other chemicals may be added to it to alter its characteristics in some fashion, the most common being pH. Water is a strongly polar solvent. It is this property that makes it so valuable.
Polarity derives from the uneven distribution of charges in the water molecule.
The electrons of the two hydrogen atoms are displaced as far from the oxygen atom as possible. This caused one side of the molecule to be more positively charged and the other more negatively charged. Consequently, the water molecules attract negatively charged ions to one side and positively charged ions to the other, enhancing solution. Ethanol Ethanol is the next most commonly used solvent. It is similar to water in that it is polar, but to a significantly lesser degree.