We've all been there. Carefully and meticulously sanding a workpiece with a random-orbit sander, going from coarse grit all the way up to 220 or finer. Thoughtfully wiping the surface clean before advancing to the next finer grit. Then to discover - after applying the finish - that there are a bunch of curly scratch marks in the wood. Back to re-sanding after all that preparation. Despite the best efforts, it's almost a given that a few grains of coarser grit will stay along for the ride, leaving the tell-tale marks in the wood.

It's hard to see these scratches in raw wood. Then when you apply a finish, it brings out the contrast - including the scratches. But the finishing phase is not the time to discover these imperfections. It's far better to spot them beforehand. There's a quick and easy remedy.

After you have sanded up to a medium grit, apply some mineral spirits or denatured alcohol to the wood to show the contrast. DO NOT use water, as that will raise the grain. Use a rag or paper towel, and don't saturate it. Just enough solvent to dampen the rag a bit. Wipe it on lightly and any errant scratch marks from the coarser grit should become more visible. Using the previous grit, go back and sand the area with the marks, brush it clean and check again with solvent. Once free of scratches, advance to the next finer grit.

Good shop cleanliness is essential as well. Between grits, make sure the workpiece has been wiped or brushed clean of any grit and debris. Your sander can also contribute contaminants. Empty the dust bag frequently (in a location away from your workpiece), and clean the outside of the tool with a brush, or a shop vacuum or dust collector hose. Use a downdraft table whenever sanding smaller workpieces to help draw dust and grit away.

The surface of stained white oak, showing the annoying swirl marks from a random orbit sander.	Stop between grits and check for scratching.
Using a rag or paper towel, wipe on a light coat of mineral spirits or denatured alcohol to bring out the contrast - and reveal any scratches.	Before resuming the sanding process, clean your sander (away from the workpiece). Don't let grit accumulate on the tool and contaminate your workpiece.