You don't have wait for years to pass to render an aged appearance to an oil painting. Although most people have to wait decades or longer for an oil painting to acquire the fetching patina of time, you can give even the newest oil painting an additional layer of pigment that will make it look as if it is centuries old. You might need to do this if you have a "shabby chic" decor style or if you are dressing a set or stage in a film or theatrical production.
Remove the frame from the oil painting and determine that it is completely dry. An oil painting will need at least six months to dry from the time of painting.
Mix oil-based varnish with a light brown oil paint in a 3-to 1-ratio in a small plastic container, such as an old, but clean yogurt container. Stir varnish and paint vigorously together with a wooden stir stick or plastic knife, until they are well-combined.
Check the consistency. The mixture should look like dark varnish and should have the consistency of very thick varnish.
Dip a 3-inch wide nylon brush in the mixture and press the brush against the bottom left corner of the canvas very lightly, dragging the brush upward. Work your way from left to right, repeating these brush strokes until you cover the entire canvas. Allow the canvas to dry for at least two days before replacing the frame and hanging.