Re: How does shoe polish work?

Shoe polish is little more than colored wax [like a crayon or candle]. Actually 
a blend of waxes with different melting points is used to obtain a balance 
between ease of application [low mp] and gloss and durability [higher mp].

The colors come from pigments dispersed in the wax such as carbon black [soot] 
for black.

When you rub the polish with the applicator brush or rag enough frictional heat 
is generated to melt the top paste layer and transfer it to the brush. The same 
thing happens again when you rub the loaded brush on the shoe. The polish melts 
and transfers to the leather. Since it is melted, it can flow like a liquid 
[although a very viscous one] and will tend to flow into cracks and scuffs.

When the polish is first applied it has a dull, matte appearance because the 
waxy surface is very rough and uneven [at a microscopic level] and tends to 
diffract light. The final buffing process with a flannel cloth melts the wax 
once again and smooths out the surface so that the leather is now glossy and 
reflective.