How to Check Sanding Progress With Pencil Marks and Raking Light

Two simple checks answer different questions during sanding. A light pencil map shows where the abrasive has made contact. Raking light reveals changes in texture, scratch direction, ridges and dents that the pencil cannot diagnose. Used together, they give you a repeatable checkpoint before you change grit.

This method is most useful on flat, unfinished wood and other surfaces where the material or coating maker permits both sanding and light pencil marking. Test first on open-pored, very soft, stained, coated or otherwise sensitive surfaces. Do not mark a final surface when the manufacturer prohibits it or when graphite could remain in pores or defects.

Know what each check can prove

Drawn lines are witness marks, not a depth gauge. If the marks disappear, the abrasive crossed those locations. That does not prove that a low spot is flat, an old coarse scratch is gone or the surface is ready for finish.

Raking light is a separate inspection. Place a bright light low to the surface so small height and texture changes cast contrast. Move the light or rotate the work because a scratch can disappear when it runs in the same direction as the light. Inspect both across and along the grain.

Norton's bare-wood sanding guidance recommends sanding uniformly, keeping a power sander moving and progressing through finer grits until the desired surface is reached. It also emphasizes cleaning dust before the next finishing step. The pencil-and-light loop turns those broad instructions into a visible stop/go decision at each grit.

Prepare one controlled test area

Remove glue, dust and loose debris before making any marks. Confirm that the current grit is appropriate for the material and defect. Norton advises starting with the finest grit that removes the imperfection effectively; beginning too coarse creates deeper scratches that must be removed later.

On a flat test area, draw a loose crosshatch with a clean, ordinary pencil. Use very light pressure. The goal is to leave visible surface marks, not press graphite into dents or soft grain. Keep the lines far enough apart that you can still see the underlying scratch pattern.

Set the light near one edge of the work, below normal overhead-light height. Dim competing light if practical. The beam should skim the surface, not shine straight down. Before sanding, note any ridges, hollows, cross-grain scratches or isolated defects so you do not mistake them for marks created by the new pass.

Sand for even coverage, not for a clean-looking pencil map

Use a flat block for hand sanding broad flat work. With a power sander, follow the tool manual, keep the pad level and let its weight and the abrasive do the work. Make overlapping passes across the whole test area.

Do not push harder on a pencil line that remains in one small location. It may sit in a hollow that the abrasive is not touching. Concentrated pressure can dish the surrounding surface while leaving the underlying geometry unresolved. Stop and determine whether the job calls for leveling the full field, filling a low area or accepting the existing shape.

For an initial bare-wood leveling stage that has been tested and genuinely needs 120 grit, eQualle 120-grit waterproof sheets in a 25-pack can be cut for a supported hand block. For a later refinement stage where 220 is appropriate, 220-grit sheets in a 25-pack provide the same full-sheet format. The pack choice does not determine the correct grit.

Browse the 120-grit and 220-grit collections for current options. Final grit depends on the wood, finish and manufacturer's process, so do not automatically take every surface to the finest paper you own.

Clean, inspect and decide before changing grit

When the pencil marks have disappeared under normal, even passes, stop the machine before lifting it if the manual requires that procedure. Vacuum the work and clean it using a method compatible with the material. Dust left on the surface can hide scratches or become contamination during the next pass.

Now use raking light from at least two directions. Look for the scratch pattern left by the current grit and for deeper lines that do not match it. A uniform current pattern is evidence that the stage may be complete. A surviving coarse scratch means you should stay at the current effective stage or step back only as far as the defect requires.

Compare uncertain marks with a known sample in the sanding scratch-pattern library. Record the grit, tool, light direction and result in the sanding grit ledger when you need to repeat the process across several parts.

Watch a scratch-pattern inspection example

This short eQualle video shows how an even sanding pattern and good inspection light help expose random-looking lines on wood. It complements the procedure above: pencil marks confirm coverage, while the light reveals whether the remaining pattern is uniform.

Repeat the loop without over-sanding

At the next grit, use fresh light witness marks only if the surface can safely accept them. Sand uniformly, remove the marks, clean, then inspect again under low-angle light. Do not keep sanding merely to spend the same amount of time at every grit; stop when the previous pattern is replaced and the planned endpoint is reached.

The pencil map tells you where you worked. Raking light tells you what the work left behind. Keeping those two questions separate prevents false confidence and makes every grit change a deliberate decision rather than a guess.