Step 1: Penetrol
He recommended a product called Penetrol normally used as a paint additive to improve flow and adhesion that also seals and stops rust. It can be used alone as a base coat on bare metal and will fix the rust while preserving the appearance. The finish will be darker than dry rust but similar to rust sprayed with water or oil and can be top coated with a polyurethane for a more durable finish.
Be sure to open and view the rest of this ible before sending me questions. ;-)
Step 2: Obey the Bot
(I originally made this a single page post since it's basically just a product recommendation but "the Bot" didn't like that. It yanked the post and sent me a note to mend my ways. So... I chopped it up and added some numbered steps. Hope it stays put this time. ;-)
1) I usually wipe down the piece with paint thinner to remove excess dirt and oil but since the product is oil based you don't need to remove every last trace. For a rusty surface I'll usually clean it real good with water and a soft brush or cloth to get any dirt off. In the case of the steel vanity tops shown in the intro I left one out in the rain for a week to cover some scratches and wanted to preserve the light layer of rust. I just rinsed it off with a hose on saw horses, let it dry in the sun then
2) applied the Penetrol with a brush. Even on the perfectly flat surface it didn't leave brush marks.
3) I always spray on a mat polyurethane top coat or two for a smooth finish and the finished piece looks completely natural.
I've used this method for several years now including on towel bars hung with damp towels everyday and for a countertop under my bathroom sink. So far they look just like the day I finished on all my projects.
Step 3: Answers to FAQs
The reason I use the polyurethane top coat(s) is that the Penetrol is a linseed oil product, and as such, is not very hard or durable. The polyurethane is a good, stable, long-lasting finish that won't easily wear off.
I've also been getting a lot of questions about clear, un-rusted metal. I wrote this about protecting and preserving the rust for it's looks. But if you don't have rust, you can skip the penetrol and just go straight to the polyurethane.
I AM NOT A PAINT EXPERT!
I'm just a guy who, by chatting with an old time paint guy, stumbled onto a way to stabilize and preserve rust without hiding it. please don't ask me how to repaint your car or patio furniture. I don't know. This post is only about preserving the beauty of rust while stabilizing it to make a rusty object useable and not so messy.
INDUSTRIAL STRENGTH POLY
A table top, specially a work table or dinning table, is a pretty tough environment. It's prone to lots of impacts and abrasion. At the least, you should use several coats of polyurethane. You might also talk to someone at a Sherwin Williams store about SherClear. It's a HD industrial clear coating. It's pricey ($100/gal?) but incredibly tough. It's made for ships and equipment but a friend uses it to coat canvas floorcloths and says it lasts for years in high traffic areas and under tables and chairs.
OIL vs. WATER BASED POLY
If you already have an oil base coat like Penetrol, you can only use an oil based product on top of it. Remember that oil floats on water. You can use oil OVER an water based coating but not the other way around. The reason is that oil based coatings don't set up completely hard but remain somewhat flexible. Water based products set up hard and inflexible and will eventually flake and peel on top of oil based coatings.