Buy a new sink.

I would skip the DIY kits and get quotes from professionals in your area. That old of a sink would be very expensive to replace with the same quality.

Dull and stained porcelain often can be brought back, but if it's chipped or eroded, there's really not much you can do. Unless some miracle has come along recently when I wasn't looking, "refinishing" is just a spray-on plastic coating that wears quickly with normal use.

Check the old-house salvage depots for an original sink from the same era in better condition. It won't be cheap, but I think you'll be happier with the results.

The thing is, even a professionally re-sprayed sink is not going to be as durable as the original. You're basically roughing up the porcelain and painting over it. The lifespan will be maybe 10 years, whereas porcelain, properly cared for, can last much longer.

But honestly, even brand new porcelain glazed cast iron is not a great sink for a kitchen, especially if you plan to use a disposal. Cast iron is strong but brittle, and porcelain chips.

I know you are here asking for re-finishing options, but your best option, as doug so elegantly put it, is to buy a new sink.

Hey Raye, here's what one looks like.

Some of the ones that look like cast iron are actually aluminium. I think they may be less durable. I’ve got a cast iron one that’s almost 100 years old and it’s in great condition. American Standard!

Mine is definitely cast iron. Unfortunately the man that previously owned our house really mistreated things and did nothing to maintain it. We have a lot of chips and pock marks in the porcelain. It doesn’t look fantastic but better than buying a new sink. Guess I’ll just say it has character and move on to my next project.

Eam44 Are you sure that is porcelain over cast iron? Looks more like enameled steel to me. Like Raye above. I have had porcelain sinks in my houses for over 60 yrs, and never had one chip. I have seen many enameled steel ones that look like the one above.

May be cast iron, but I don't believe it's a hundred years old. Twin compartments and 4" strainers are relatively modern inventions.

I assuming that somewhere is a craftsman who is capable of refinishing the sink but since the refinished sink will look like a new sink, why not just put in a modern sink? Is there something special about the design that isn’t available in a modern sink?

Related question for my 80+ year old cast iron tub - what’s the best way to remove stains and discoloration?

I don't think that is a 100 year old sink either. I would replace it.

Our cast iron tub was sandblasted and repainted about 4 years ago. It was good for about 3 years but has now started to peel :-(

Em didn't say hers was 100, the op did. The process to bake porcelain onto cast iron basically requires a blast oven to bake enamel on. I doubt there is anyplace feasible to redo it, if there is probably very few and expensive. Like OP said, may live with it.

My husband has used some stuff on our car, for very small rust spots don't know what it's called though. It's supposed to stabilize and stop the rusting process and seal it. I wonder if something like that might work, then just spot cover with home fix it kits. Maybe better than nothing if you really want to keep it.

Yeh, I lost track of who said what.

https://www.houzz.com/discussions/2674343/re-finishing-old-sink

Ten years? Pfffttt. Maybe ten minutes. Sinks can't be refinished.

Izzy, that's Bondo that is used on cars.

It's not Bondo, a filler, unless they have a similar product. I looked up what it could be. I am sure it was this type of product, rust converter.

https://shop.fertanusa.com/shop/rust-removers/fertan-rust-converter/