TIBETAN SILVER is a metal alloy made of zinc, copper and tin. It is lead free and nickel free and will be OK for most people with sensitive skin.
SILVER PLATED sterling silver layer, plated over a base metal, usually copper.
GOLD PLATED Thin layer of usually 22k gold plated over another metal
PEWTER is a soft metal alloy, mostly tin, that has a darker 'antique silver' look to it. It will bend with a bit of force.
RHODIUM PLATED Chrome-like, precious metal with high shine. Most 'white gold' is rhodium plated.
STAINLESS STEEL chains do have a small nickel content, avoid products with this metal if you have any nickel or metal allergies