MadSci Network: Chemistry

Re: why does nail polish dropped in H2O, float on top of the H2O and dry?

Date: Sun Mar 15 23:18:02 1998
Posted By: Ken Johnsen, MadSci Admin
Area of science: Chemistry
ID: 889976029.Ch

Dear Caitlin,

Nail polish in the bottle has three main ingredients: pigment [the colored 
stuff], binder [the glue that holds it onto your nail] and the vehicle [the 
solvent that makes it all a liquid].

The "sink or float" property is determined by density, how much a given volume 
weighs. Most pigments are denser than water and sink. Most binders have about 
the same density as water and will be suspended, most solvents [at least those 
used in nail polish] are less dense and will float on water.

The density of the liquid polish is simply the fraction-weighted average of all 
three major ingredients. Since liquid polish floats on water, the density must 
be less than that of water.

Once the polish is floating, it is easy for the solvent to evaporate to the air 
[this is the odor you smell when doing your nails]. The colored glob left 
behind is really no different that the color on your nail. If it doesn't sink 
either, then it's density is also lower than water [only now the density is 
computed from only the pigment and the binder.]

What lead you to think that nail polish was denser than water in the first 
place? When an experiment disagrees with a supposition, it is very often 
because the supposition was false. This is the very essence of the scientific 
method. Thank you for your question to MadSci Network!

If I can help any more, please send me an e-mail.



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