It's unsuitable for steel baths (and cheaper to buy a new one), but if it's a special cast-iron bath it'll be as good as new, with a very durable finish.

Edible drying oils such as hempseed oil, walnut oil, and flax oil are used to create a more durable finish.

Cured polyesters can be sanded and polished to a high-gloss, durable finish.

Nitrocellulose lacquers produce a hard yet flexible, durable finish that can be polished to a high sheen.

These lacquers produce very hard, durable finishes that are both beautiful and very resistant to damage by water, acid, alkali or abrasion.