The string on the electric guitar lays on two points: the nut and the bridge saddles.
The nut can be made of many different materials according to the quality and tone we want to achieve such as:
various plastic materials the likes of Micarta, Corian, ect.,
metal (most of the times brass or steel),
other lubricating materials such as graphtech.
Various types of nuts (photos thanks www.stewmac.com).
In terms of tone the material the nut is made of, influences the tone of an instrument on the open strings
and on the difference between them and the fretted strings.
What we are looking for here is that the open strings sound the most possible like the fretted ones.
The best way to achieve this is by using a so told "zero fret" meaning a fret which is installed in place of the nut
with a sort of strings guide behind which holds the strings in the correct position.
Another way to achieve this is by using a metal made of materials such as brass or steel.
An LRS steel nut and a zero fret.
Here is a brief list of each material and its tonal feature:
Bone. Bone is in my opinion by far the best material to be used for nut construction as it features
volume, a wide open tone, strength against mechanical shocks and offers a fine tuning reliability especially if periodically
Ivory. This is very similar to bone but a bit harder and brighter and a bit more difficult to craft.
Micarta, Corian, TusQ, etc. These are plastic materials of various hardness and density.
Some of them sound and react pretty like the bone even if they hardly reach its sustain and tone articulation.
Graphite. The use of graphite is almost a must in case of a guitar equipped with tremolo.
The tone is well balanced and graphite is a good compromise between tone and performance
Graphtech. This material is made of graphite mixed with teflon which feature a better lubricating and a better tuning stability
in case of tremolo use. The sound is very close to standard graphite.
TusQ. This is a synthetic material that sounds more close to bone.
It's made of polymers pressed at very high temperature to reach such density of the bone itself.
Brass. Being almost the same material of frets, brass ensure your fretted notes will be identical to
the open ones. A brass nut will also last for years with a minimum or no maintenance at all.
A bit hard to work but it's worth th effort.
Steel. There's some offer of steel nuts as well around. The are most of the times equipped with rollers to ease the strings slide.
Like brass, steel is another fine material for nut if you're not after the classic "vintage" tone and you wish for some more
A brass nut on the Exlusive "Shredder" model.
The video below shows how a nut should be made. This video is a part of a series of 5 footages explaining the perfect strat setup for tremolo.