Finishing a wood window cornice is the same as finishing any other unfinished wood project. It requires the same tools and techniques and is an easy job for a do it yourselfe.
Step 1 - Prepare the Wood
Be sure the wood is free of all dirt, dust and stains. You can sand the entire piece lightly with the sandpaper then wipe it clean of sawdust with the tack cloth. This will make a good surface for the wood stain to adhere to. Be sure to do the edges and ends also, basically any surface that will be stained.
Step 2 - Stain the Wood
Stir the wood stain to mix all the pigment in the bottom of the can. Dip the brush into the stain and spread it on the wood with the grain. Let it sit for 10 minutes or so then wipe away the excess with a clean rag. If you want the finish darker, repeat this step.
Step 3 - Varnish the Wood
When the stain is completely dry, apply a coat of varnish. Do not shake the varnish can as it will create bubbles that can ruin your wood piece. Brush it on with the wood grain and let it settle and dry. Usually one coat of varnish is all that is needed for a project like this.