The hand, what a great mystery!
It should be noted that this part of the costume was very unpractical, as the material and design of the hand gave very little room for movement. From the study of behind the scenes pictures, different pictures from exibitions and clips from the movie, it seems like two versions were used in ANH.
Type 1, probably being the one used for the-pick-up-comlink-scene in ANH (see embedded video later on in this post) with separate fiberglass(?) fingers and hand plate over a glove. This type of glove is also seen in the pre-ANH prototype versions as featured in the Star Wars Visual Dictionary.
Type 2 being cast as one piece in some kind of urethane or rubber, and is used extensively throughout other parts of the film. The type 2 hands are also seen to be used for ROTS. The distinguished characteristic of the type 2 hands is its ability to hold its shape, which makes them easy to spot in the movie.
The picture below is from Steve Sansweet’s book “Star Wars from Concept to Screen to Collectable”, and shows the hand in detail. However, it seems to be type 2, and not the type 1 version.
The picture below shows the newest type (ROTS?) of glove, which is of the type 2 version, and made in some kind of flexible urethane material. My guess is that the hand is made in one mold, with the gold parts spray painted on with chrome spray similar to Spectrachrome (which is flexible).