[klondike98]

I think you are talking about grain filler which is used to fill the grain in wood such as walnut. You see the grain in oak as well. If you don't fill the grain with grain filler you can also do it with many coats of lacquer and sanding but grain filler is easier (for me anyway). It takes some skill to do the job correctly and there are some threads on here that talk about it. Several brands of filler have been discussed including Constantines sells some though the WoodPerfect brand I see there seems different than what I remember. Another brand is Pore o pac, which you can find on amazon. I've used Timbermate as well.

If you don't use grain filler you will be able to see the pits/holes/ that are not level with the rest of the surface of the lacquer. Sometimes it takes several tries to get the surface smooth enough for the lacquer phase and I have yet to be able to do it perfectly. Some of our better refinishing folks will surely chime in as well.