Pin vices are generally made from steel or nickel plated steel which is corrosion-resistant.
The nickel plating not only makes the tool rust-resistant but also gives it a harder coating to further maintain its life.
English pattern pin vices are made from steel that has been further hardened by a black oxide coating. The black oxide coating gives the vice a hard protective layer that is corrosion-resistant. Black oxide is a cheaper protective coating compared to the more expensive nickel plating.
Aluminium
Swivel-headed pin vices and push pin vices can also be made from aluminium. This is also corrosion-resistant and hard-wearing but can be more expensive than nickel plating.
Brass finish
The Archimedes drill is primarily made of breass but is also available in steel. Brass is hard wearing and, to an extent, resistant to corrosion.
Which material is best?
Aluminium vices may be slightly more expensive than nickel-plated vices, however, both are hard-wearing and rust-resistant so which you choose is likely to be down to personal preference.