Raw linseed oil -- derived from flax seeds -- is an non-drying, edible product, but the linseed oil you use for wood finishing has been "boiled" by treating it with chemicals. Compared to raw linseed oil, boiled linseed oil hardens fairly quickly upon exposure to air, which is why it's one of the main components of traditional oil-based paints and varnishes. Once it hardens in the wood grain, it can be as difficult to remove as paint or varnish. However, because it doesn't penetrate that deeply, you can usually do the job with a combination of solvents and sandpaper. While getting linseed oil off a finished or non-porous surface is a snap, it may take some effort to get it out of porous stone surfaces, such as unfinished marble or granite.
Removing Linseed Oil From Wood
Once linseed oil has hardened in the wood grain, you may be able to soften it with mineral spirits, but, if not, use lacquer thinner.
Moisten rag with mineral spirits and apply the solvent liberally to the wood. Give it a few minutes to work; then rub vigorously. Wait for the solvent to dry; then determine the degree of your success by examining the color of the wood. You got most of the oil out if the wood is significantly lighter in color than it was before. If you don't notice much change, you need more aggressive removal methods.
Sand the wood by hand or with a machine -- depending on the amount of surface area you need to cover -- using 100-grit or finer sandpaper. This wears down the surface layer and provides access to the deeper grain, where the oil may have congealed.
Wipe down the wood with lacquer thinner. This is a volatile, flammable solvent, so wear a respirator and avoid heat sources while using it. Soak a rag with the solvent, spread it liberally onto the wood, and rub vigorously. Repeat as many times as necessary until the wood lightens and all traces of the oil are gone.
Removing Linseed Oil From Natural Stone
When it soaks into stone, linseed oil continues to attract dirt, and if you try to rub out the oil with a solvent, you're likely to grind the dirt deeper into the stone. To avoid this, apply a poultice to draw out the oil.
Moisten the stained area -- and a region that extends well beyond it -- with liquid laundry bleach. Omit this step if the stone is dark, because bleach will lighten it.
Make a paste of baking soda and water. Spread a 1/4-inch layer over an area that encompasses the stain and a region beyond it, using a plastic or wooden spatula.
Cover the paste with a damp cloth to keep it moist, and leave it overnight.
Remove the paste, using the spatula to scrape it off, and rinse the area with clean water. Blow the area dry with a hair dryer and look for residual staining. If you see any, repeat the procedure.
Removal From Non-Porous Surfaces
You can usually remove tacky linseed oil from any non-porous surface by washing it off with soap and hot water. If the oil has dried, moisten the rag with mineral spirits, which is safe for virtually every type of painted or finished surface. In rare occasions when that doesn't work, try isopropyl alcohol or acetone, but test these solvents on the finish before spreading them over a wide area.