I had a steel shelf made to go over my stainless-steel stove. The shelf is not stainless, just plain steel, and it has bright, shiny spots where the parts have been welded (soldered?) together. I understand that the steel will rust with time if it's not sealed. I want to make the shiny spots the same color as the rest (dull grey) and then finish the whole thing so it won't rust. I'm no expert. Any advice?

Is this galvanized or regular steel?
You can check with the fabricator to be sure.

It's regular steel. The company that made it does the industrial look, and apparently many residential customers who live in loft-like spaces prefer the rusty look the steel gets after a while and are fine with the roughness of visible soldering. My kitchen is more traditional/modern, so I want the shelf to look as much like stainless steel as possible to go with the refrigerator and stove. My hardware store said just to paint the whole thing with Rust-oleum paint in a smoke gray. I'm hesitant to do that because I do like the color and sheen of the natural steel (it looks a lot like stainless now) and once it's gone, it can't be brought back. Many thanks for any advice you can give.

The problem you have is the rusting of the metal and if you just put a clear product on the metal it may still rust, and then you would have a very hard time stopping it.

What you can do is prime the metal with a rust resistant metal primer (oil based) and then topcoat it with a paint that is close to the stainless steel look. I pretty sure you can find one in a spray or maybe a brush on paint that will work for you.

Hope this helps out.