Furniture or panelling made from knotty pine stands out, which is good if you like its bold, rustic appearance. If you decide to change your decor and the look of knotty pine no longer fits with what you want, you can paint it to blend in. The hard part is subduing the stubborn knots, which can reappear as brownish circles when they slowly bleed through the paint. With proper preparation, however, knotty pine looks as good painted as any other wood.
Fill cracks in the knots with commercial wood filler. Scrape the excess wood filler from the surface with a putty knife while it's still wet, then let the filler dry.
Sand the wood using sandpaper on a sanding block if you're working on a flat surface or held loose and shaped to the curve of the wood if you're working on a curved area. Start with medium-grit if needed and finish with fine-grit, paying special attention to smoothing the knots and the areas around them. Wipe off the dust left from sanding with a damp cloth and let the surface dry.
Brush or spray natural shellac diluted with alcohol over the knots. Let the shellac dry, sand it lightly with fine-grit sandpaper, then add a second coat over all the wood. Let it dry and sand it lightly again. Add a third coat if you want extra assurance against the knots bleeding.
Paint the wood with a primer, either oil- or latex-based depending on what kind of paint you've chosen for the final coat. Use a brush, spray or roller. Let it dry, sand it with fine-grit paper, and dust off the grit with a slightly damp rag.
Paint one or two final coats of latex or oil paint, allowing time to dry between coats. Sand lightly between coats for an extra-smooth finish.
You can buy natural shellac in spray cans or ready-mixed, but check the expiration date to make sure it's fresh, since pre-mixed shellac deteriorates over time in the can. Because shellac is alcohol-based, it isn't affected by the turpentine in the knots, so it blocks the knots from bleeding through the finished paint.