Staining wood is the process of letting a very thin, watery pigment sit on it long enough to soak into the grain and accent the natural designs of the wood, before wiping off the excess. "Pickling'' refers to a specific kind of staining process that uses regular white paint that is thinned out and applied as if it is regular stain. The effect is a translucent white finish that shows the natural beauty of the wood while giving it an antique-looking patina. Knotty pine is especially good for this kind of treatment because of the interesting patterns in the wood.
Strip, sand and thoroughly clean the wood to be stained. Lay rags around the bottom of the wood to catch runoff from the stain.
Mix your primer in a can with with an equal amount of water. Stir well.
Spread the primer-water mixture generously over the knotty pine with your brush, pushing it into all the cracks and corners.
Let the stain sit for five minutes, then wipe it down with a slightly damp rag, pressing lightly to leave the white residue on the wood. Let dry for day.
Coat the wood with clear gloss to seal in the pickled stain.
If the stain looks too heavy to you when you wipe it down, wipe some more. If it looks too thin, apply another coat before it dries.
Make sure the room is ventilated when you apply the stain and the gloss.