I've never seen any real contrast to speak of once the barrels have been through a number of rusting and carding passes. You have rusted and browned both the steel and the iron. Any initial contrast gets very muted or disappears altogether as the barrels become darker. Both rusted surfaces will convert to black during boiling if you are shooting for black and white, which is correct for a Lefever. Iron rusts easily, and it is the iron content of the steel that oxidizes to become hydrated ferric oxide, or common red rust. The contrast is brought out during etching with ferric chloride solution. A lot can go wrong during etching. I feel it is better to use a weaker solution because going a bit too strong, or a bit too long can remove a lot of what you worked so hard to achieve. Even using a vertical tank for etching can be a problem because the end that goes in first is the end that comes out last. That extra few seconds can lead to less contrast on that end of the tubes. You also have to work quickly to rinse and neutralize the ferric chloride solution after your etch cycle, because it is still working to remove rust until you rinse and rub it off the surface.
One thing you will learn is that there are no perfect instructions that work with all steels and all barrels under all atmospheric conditions. You will have to constantly adapt to find what works best on a particular set. What works great in a humid week in August may be a problem during cold dry winter months. You can learn a lot by experimenting with some pieces of junk Damascus barrels, by trying different rusting solution, different rusting times, use of a pre-etch prior to rusting, different concentrations of ferric chloride, different etch times, and varying when you etch after so many passes etc. Unless you are doing this all the time, it helps to keep a notebook of what worked and what didn't. When you screw up, you can strip and redo your short section of junk barrels rather than messing up Grandpa's Lefever or Parker. There is a very good reason why it costs upwards of $300.00 for a nice rust blue job on a set of barrels. The materials are cheap as dirt, but the labor and learning curve is steep.
