I just finished some knotty pine planking for an entertainment center where I had to match the existing finish. I don't know what products are available where you are, but I started out by sanding with 100 grit, NOT using an orbital sander. You don't have to sand much, just to rough up the surface a little. Then apply some Minwax sealer and surface conditioner. Follow the instructions and then put on a coat of Minwax Puritan Pine woodstain. This approximates the patina that would exist on a piece of old wood. Wait 12 hours and apply an orangey, yellow varnish stain like Benjamin Moore Early American. This is a very good varnish stain that will dry enough for sanding under normal conditions in 6 hours. The more coats of varnish stain you apply, the darker the wood will get. I found that 2 coats did it. The sealer is very important if you want an even finish. You can't tell the new wood from the old. If you'd like to see what happens if you forget to apply the sealer first, go to
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The board on the left has no sealer and look at how splotchy it is. The picture was taken after the coat of Puritan Pine, before the Early American.