Step 2: Obey the Bot
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.