What are most vintage claw foot bath tubs made from ?
Any concerns with the inner tub being worn/chipped, in regards to chemicals or veneers leaking out when in use... or does it have to be refinished ?
In this specific case will be using it as an ice bath and no plumbing connected. Any issues with using water\ice in the 45-55F range?
Most are made from cast iron with an enamel baked on finish.
The enamel protects the cast iron from rusting. If the cast iron is showing, then it should at be at least protected with a good paint. Imagine the tub not looking like new is not an issue.
About the only issue I would have using it for an ice bath, is that it is cold. Cast iron bathtubs are known for holding the water temperature longer(at least for warm water), than the new thinly made tubs. Do not think there are any concerns of chemicals/offgasing, even if they are chipped. The chips might be sharp enough to cut if not removed(loose chips).