When you're making an actor into another person you must alter his appearance so it fits the new character.If the character is mean, kind, fat, thin or ugly you must change the actors own features to match this.
To be able to do this we use a lot of different methods such as wigs, false teeth and facial prosthetics.
When you're doing a highlight and shadow makeup you are really just using the actors own features to alter his looks by showing and hiding things that are already there.
Some actor once said that all parts are an insult, because the makeup artist always bring out the "bad" bits of the face when doing a character makeup.
Depending on what kind of stage you are working on the makeup can differ quite a bit.
If you're working on a small stage you have to put on makeup which is very subtle but for a big stage it can look really grotesque in person but great on stage.
Character makeup can also sometimes be classical makeup's like the Peking opera masks or Japanese kabuki makeup.
These kinds of makeup are very hard for us to understand and do correctly because they come from thousands of years of tradition.
Every colour and line means as much as a whole book of knowledge.
All we can do is mimic or do our own interpretation which is bound to be wrong.