You can use radiator paint. You should be able to find it in your local hardware store.

the tub in the post is probably not painted. it appears to be a metallic film, or aluminum cover. or perhaps, the tub is originally that color, and the inside was painted white! GOOD LUCK!!!

OR. you can use silver leaf with a coat of polyurethane.

Silver leaf would be brilliant...

perhaps not the sheen you're looking for, but i've found the below combo to be *very* durable (albeit somewhat expensive). it gives the look of silver auto paint (like on a silver car). applied correctly, it looks/performs to almost body-shop quality.

http://www.autopia-carcare.com/wus-892181.html
http://www.autopia-carcare.com/wus-893351930.html

That looks lovely! I think having the tub powder coated could be possibility.

Lesly, I think that you'll need to use an oil-based enamel. I recently used a metallic enamel by rust-oleum that I bought at Home Depot. The enamel will stick better to the slick surface of the outside of the tub, and it's more durable in high heat situations (hot bath). It's only about $25 a gallon, and you'll probably only use about 1/3 or the gallon.

I just did a project using this paint. http://etrine.com/2008/07/14/bookshelves/
If you like the finish, then I think it's the way to go for you.

I agree with eddivegas, the outside of the tub does look like unpainted aluminum, or a galvanized steel. The Rust-Oleum paint I mentioned can be applied directly to that metal.

Go for it.

I used Rustoleum paint on the exterior of my cast iron tub, and it's worked very well. They have a line of metallic spray paint - I would try that.

I just finished this project, using silver leaf and clear coat of poly- acrylic.It is bee-u-tiful.

Yeah, this before/after on Domino said they used silver leaf on a claw foot tub.

The best metallic paint I've found is an artist mural acrylic from Nova Color (http://www.novacolorpaint.com) The paint is thick and the colors are rich. Because it's acrylic, it cleans up with water but dries waterproof. I've used antique gold (greenish), royal gold (orangey gold), bronze (pink gold), antique copper (deep red), copper (orangey red) on walls, ceilings, book cases, faux wainscoting, trim, mirror/picture frames, a clawfoot tub and cast iron feet. This stuff is amazing. I've used it throughout my home. Unfortunately, the only way to see the true colors is to order a free color chart of paint samples. Still, the color chart is free. This stuff is truly amazing. A gallon lasts a very long time. I'll post some pics soon. I did my tub in antique gold and the feet are in all of the other colors I mentioned above. This stuff is the best.

Most of the metallic spray paints I have tried rub off. Can anyone suggest any that don't? I think I am going to try automotive spray touch up paint - it seems like that should be more durable, although probably more toxic!