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I'm an absolute beginner to woodworking, so apologies if my terminology is wrong/inconsistent.

I have been making a dice holder box, and have gone onto the sanding procedure. Using sanding paper with a grit range of 80/150/250/400, I've been smoothing the edges of the box. It's been taking a long while, which makes this issue a bit frustrating.

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I have tried blowing, washing and more sanding in an effort to get rid of these marks - but I'm worried I might worsen the problem. Could anyone please give some advice? Many thanks.

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  • Hi, welcome to StackExchange. "grit range of 80/150/250/400" Ok first off there's nearly never any benefit to sanding beyond about 180-240 grit. A lot of people do it, but very frequently it's not actually yielding benefit (even if they think it is). Now that aside, you appear to have done a very good job on the sanding from what I can see, it may be just that the paper itself caused the issue. So your 400 grit paper (and possibly others) could be the culprit — are they dark grey? This is generally wet 'n' dry paper, and not intended for sanding wood. – Graphus Apr 3 at 10:15
  • Thank you for the quick reply! All the sanding paper I used is black / very dark grey - your answer does make a lot of sense. Looking at the back of my two varieties of sandpaper they say the following: 1) aluminium oxide waterproof abrasive paper 2) silicon carbide waterproof abrasive paper electro coated. I'll look for sanding paper specifically tailored for wood as you suggested! – D C Apr 3 at 15:41
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    The silicon carbide stuff in particular is problematical for wood because of the inherently dark colour of the abrasive grains, and the fact that they break down in use (they're supposed to, as this reveals fresh sharp edges as the paper wears) which releases dark grey dust which can easily become lodged in wood. Just to note abrasive paper (or cloth, or screen/mesh), for woodworking is not all the same colour. Aluminium oxide abrasives are sometimes a natural brownish colour, but many are coloured in some way however these tend to leave no coloured residue in/on the wood. – Graphus Apr 3 at 18:44
  • I would use a random orbit sander with a 80 then 120 grit on tan paper with the ends and corners over the foam pad with some but not too much pressure in constant slow motion using a vacuum hose attachment.. 50kRPM Rockwell’s do a much quicker job than the typical 20k~30kRPM – Tony Stewart Sunnyskyguy EE75 Apr 4 at 5:51
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As clarified in the Comments, some of the abrasive used was silicon carbide paper (wet 'n' dry). The abrasive grains on this kind of paper fracture during use1, releasing a very fine grey/black dust. On the hard materials wet 'n' dry paper is suited to2 this dark residue isn't a problem, but obviously on wood it can become lodged in the surface. On some softer or more open-textured woods the dark staining can be much worse than this.

You can try to scrub it from scratches or divots in the wood surface using a very stiff brush like a toothbrush, or even a fine wire brush, but my experience has been this is almost never 100% effective. And on end grain it simply doesn't work. So unfortunately the only effective way to deal with this is to remove the affected wood; file, scrape or sand until you've gone deep enough that the stains are gone.

When you're faced with such a task on a well-sanded piece like this almost everyone doing it by sanding is tempted to stick with a finer grit, to avoid creating deeper scratches again. But this is a false time economy — you spend more time sanding at higher grits than you would starting with a coarser grit (which removes material so much faster) and then working through your progression of grits to successively remove each previous stage's sanding scratches.


1 Which is as intended, fracturing reveals fresh sharp edges on the grit particles which continue to cut well as the paper wears, in contrast to aluminium oxide abrasives which tend to round off during use and progressively slow

2 Which includes hard finishes used in woodworking (including shellac, varnish and lacquers) when aiming for a very flat surface and/or working towards a super high gloss or 'piano finish'.

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