Mild Steel is the authentic choice for chainmail. It is the material that was historically used for chainmail armour since its inception.
It has a very dark grey/brown colour and is not shiny due to a very thin oxidisation layer that forms on the steel (rust).
The advantage of mild steel is in its strength and its authenticity.
Its disadvantages are that a full mail shirt is very heavy (anywhere up to 20kg/3 stone) and it will rust if not looked after.
Rusting may not be too much of an issue if you use your armour on a regular basis. Due to the rings rubbing against each other when you move any rust is cleaned off. Chainmail shirts are often referred to as self-cleaning, this is only true if used regularly. If you are wanting to store mild steel armour for any length of time, a light coating of oil (WD40 will do) is necessary.
I only use mild steel for making authentic armour suitable for battle re-enactment and Live Action Role-Play (LARP). It is unsuitable for jewellery.
Mild steel shirts and armour are custom only orders. Please contact me for details.