The issue is dust and lint that falls onto the painting or is deposited by linty brushes or rags. It doesn't seem so bad when the paint is wet, but the surface of the dry painting seems to show the impurities more as the paint film dries.
I usually spend time at the beginning of a painting session blotting up any stray lint on the previous dry layers with a piece of semi-sticky tape, and then again at the end of the day using a tweezer in the still-wet layer, but I still end up with lots of debris. It might not matter for some painting styles, but for detailed glazing on a smooth panel it can be a big problem.
So I got a tip to try wet sanding and it worked really well for me. Here's what I did:
Materials:
- 1200-1500 grit wet/dry sandpaper
- linseed or other painting medium oil
- small bowl for the oil
- clean, lint-free rag of synthetic material - a microfiber eyeglasses cleaning cloth works great! (cotton rags and paper towels have too much lint)
I used 1500-grit "wet/dry" sandpaper, moistened with a bit of linseed oil. I rubbed any area of the surface that was imperfect: too much medium, or a piece of embedded fiber or dust. It worked really well, I was amazed how the imperfections were healed by the process - most debris lifted right out and left the colors of the painting intact. Small unintentional drips or ridges sanded right off easily. I had to do a bit of touch-up painting in a few areas, but the process was a huge success.
I did the wetsanding on fairly-dry areas - maybe a week of drying. Dry to the touch, but you could probably still gouge or dent the surface if you tried. I was also willing to repaint whatever I messed up. (I wouldn't try it for the very first time on a masterpiece you thought was done and no longer have reference for, in case a little repainting is necessary.)
I was actually surprised how much I could rub and disturb the surface, and still the colors of the paint would remain. In some places the surface fogged up a tiny bit but was pretty resilient. I did leave a very thin layer of oil to restore the gloss in some areas (although I know some people say not to do that and just wait till varnishing.)
Also, it's not sanding like you sand a piece of furniture - I used a tiny folded square of sandpaper bent over one fingertip and pressed very VERY gently and rubbed in a very small area, only in areas that needed it.
Once I sanded I had a yucky layer of wet oil and loose lint, so I needed to find a lint-free way to wipe that off. I found what worked best was a microfiber eyeglass-cleaning cloth I bought at the local hardware store. I could wipe firmly enough to wipe off the wet oil and dust, without leaving additional lint dust like a paper towel or cotton rag would have.
Also, it's not sanding like you sand a piece of furniture - I used a tiny folded square of sandpaper bent over one fingertip and pressed very VERY gently and rubbed in a very small area, only in areas that needed it.
Once I sanded I had a yucky layer of wet oil and loose lint, so I needed to find a lint-free way to wipe that off. I found what worked best was a microfiber eyeglass-cleaning cloth I bought at the local hardware store. I could wipe firmly enough to wipe off the wet oil and dust, without leaving additional lint dust like a paper towel or cotton rag would have.
Of course, a linseed-oil soaked rag is not good to leave around (serious fire hazard), so I washed it in natural turp and then soap and water at the end of the day... so it adds some steps to my normal cleanup.
One more tip: An accomplished painter I know just recommended using "shop cloths" as studio rags. They are extra heavy duty blue paper towels on a roll, I found them in the hardware store. They are amazingly lint-free. I had previously been using well-washed flour-sack dishcloths, and they seemed pretty lint-free but I now suspect they were adding to my dust problems - I seem to have a lot of very tiny white filaments flying around my studio. I'm going to try the shop cloth for a while for wiping brushes while I paint and see if that helps reduce the dust in the first place. (But I still would only use the microfiber eyeglass-cleaning cloth to actually wipe the surface of the painting.)
One more tip: An accomplished painter I know just recommended using "shop cloths" as studio rags. They are extra heavy duty blue paper towels on a roll, I found them in the hardware store. They are amazingly lint-free. I had previously been using well-washed flour-sack dishcloths, and they seemed pretty lint-free but I now suspect they were adding to my dust problems - I seem to have a lot of very tiny white filaments flying around my studio. I'm going to try the shop cloth for a while for wiping brushes while I paint and see if that helps reduce the dust in the first place. (But I still would only use the microfiber eyeglass-cleaning cloth to actually wipe the surface of the painting.)
Let me know if you have any additional tips for cleaning the surface of your painting or dealing with dust in the studio.