Put on rubber gloves to protect your skin.
Wipe down your rolltop desk with oil soap, using a clean rag. This will clean your rolltop desk and remove any skin oil and dirt.
Clean the oil soap and residue off the rolltop desk by using another rag dampened in mineral spirits. Allow the mineral spirits to evaporate off your desk.
Sand your rolltop desk with ultrafine sandpaper to get any scratches off the surface. Sand in the direction of the wood grain for best results.
Clean the sand dust particles off with a tack cloth and then rub your desk with a steel wool pad to finish the sanding process. Wipe off once more with tack cloth.
Apply a coat of furniture oil finish to your rolltop desk with a brush, using an oil finish that best matches your furniture's color. Brush on with the wood grain, just as you did when sanding. Let it soak in and dry for about 30 minutes or as long as recommended by the manufacturer.
Apply a second coat of oil finish to your rolltop desk with a steel wool pad to get the oil finish to penetrate into the wood grain. Let the second coat dry.
Dampen ultrafine sandpaper slightly and sand the second coat, then apply a third coat of oil finish to your desk with a brush and allow to completely dry. Buff thereafter with a clean microfiber cloth.