June 18, 2003
A: FROM MENTOR SHEILA ENGLAND IN PA
Answer from my son-in-law who has his PhD in Chemistry:

Do searches on either thermochromic pigments or goniochromatic pigments,
these are the most likely types to be used in nail polish. Thermochromics
are materials that change color due to temperature, like mood rings.
Goniochromatic materials change color depending on the angle at which you
look at them, like some car paint.

The thermochromic materials actually undergo a reaction upon heating.
Usually this is just a re-orientation of the bond structure, maybe a linear
molecule would become bent. Other thermochromics will gain or lose an
electron to become a salt. The third type of thermochromic would be liquid
crystalline, similar to the little adhesive thermometers.

I could conceive of solvatochromic nail polishes (something that changes
color in different solvents). These would, for example, be green when they
were wet and turn to blue when they dried, but I don't know whether anyone
actually produces them.