When most people think of a pickled finish, they think of a white or off-white finish. Actually, pickling is a method that gives color to the wood, while allowing the grain pattern to show through. Wood can be pickled any color that you want.
Practice on a piece of scrap wood that is the same species as your workpiece, as different wood species produce different pickling effects.
Before you pickle the wood, you should seal it. Use a quality sealer such as Parks Sanding Sealer. Apply the sealer according to the manufacturer's instructions. After the sealer is completely dry, sand it with #200 sandpaper to remove all roughness.
Clean your project and wipe it off with a tack cloth.
For the actual pickling, you can use oil base paint that you have mixed 50/50 with mineral spirits. Be sure to thoroughly mix this solution.
Apply your solution with a good quality paintbrush. Try to avoid runs, but apply a heavy uniform coat.
You may have to experiment with the amount of drying time, in order to get the desired color.
Use lint free rags to wipe off the excess solution. Wipe with the grain. Let the piece completely.
Next, you need to seal the piece with polyurethane to permanently seal it. Apply even, thin coats with a good quality brush. After the first coat has dried, re-clean the piece, sand it with #220 sandpaper, and re-clean it with a tack cloth. You need to repeat this process until you have a minimum of three coat of polyurethane on your project. Between coats, use progressively finer grit sandpaper.
If you follow these steps and clean the project as outlined, you will end up with a great pickled finish.
A note of caution: Make sure you are working in a well-ventilated area and properly dispose of your paint rags.