It's History How could anyone come up with the idea of using the excretion of the female Lac beetle, in a fluid suspension as a finish? Extraordinary, but, this is in essence what French polish is, a mixture of this excretion and methylated spirits or wood alcohol.
Generally considered, a polish of French origin, as the name would suggest.
This is because it has been attributed by use, to the Simon brothers in Paris in 1730's.
 However, the use of this type of finish, predates this, as traces have been found on objects in ancient Egypt, China and Rome.
As a polish, shellac has a very pleasing visual and tactile quality.
 As a practical average 'battleground/household type finish (if my home is anything to go by!) it is quite limited.
The problem is that shellac doesn't stand up well to liquids being spilt on it!  As well, the finish is brittle, by nature, and won't resist hard knocks.
To the general public, and a lot of wood finishers, french polish is a finish like paint is a finish.
But, like paint you can get different kinds, with differing varieties of use and appearance.
The Cut To begin with, you can get differing solid content.
This is measured by the proportion of shellac flakes to it's carrier, methylated spirits.
This is known as the cut.
 For example, a 5lb weight of flakes to a gallon (5 litres) of spirits, is called a 5lb cut.
The less the percentage of flake, the thinner the shellac will be.
You would select the cut for the job in hand.
Ideally you would mix the polish, as and when required (it has a rather short shelf life).
This is quite straight forward, as there are only two ingredients involved! You would mix the polish 24hrs before you would use it.
 Do bear in mind that the meths you would normally get in a hardware store would be coloured.
 Ideally, you would use un-tinted spirit to mix and this can be hard to get.
Of course you can get it premixed, and for most of us this is perfectly acceptable.
But, as I have mentioned, don't buy much more than you would use in a three month period.
What isn't generally realized too, is that you can get a selection of different coloured flakes.