Not ceiling, but knotty pine paneled walls are what I painted white. What I found afterward is that cracks and gaps and imperfections are more visible because they show up as black, and the painter that I hired only filled a couple and also made the mistake of using the wrong caulk in the few worst holes that he addressed (that couldn't be sanded) so they were just as obvious. So, after he was done, I did have to go around the room and caulk the worst gaps in corners, under the ceiling trim, and between some of the boards (only a few of those though!). Then used spackling in the most obvious open knots -- and then touch up the caulked/spackled areas.

In the end I do like how it turned out. I can see some imperfections because I know they are there -- I am not sure any casual observer would notice -- and other imperfections are just part of the knotty pine look, painted or not.

If I were doing this myself from scratch, I would caulk any obvious gaps, then try to use a good primer that is meant to fill and smooth uneven surfaces (I believe that Sherwin Williams makes one) although I don't know how well that would work against gravity on a ceiling. Be prepared to do some extra filling and touching up once the final coat is on and dry in case you see anything that bugs you.

You are opening a can of worms.

How high are the ceilings?

Why are the beams blue?

What's going on with the actual living space from the floor up 7 or 8 feet? Is everything perfect there? If not then concentrate of the living area and leave the ceiling alone for now.

You would prime before caulking anyway. I would use BIN since it is a good primer and will take care of the knot bleed. After it is primed, you will be able to see the gaps more clearly and decide how much caulking you want to do.

Thanks everyone. To answer a few of your questions, These ceilings are in our kitchen and living room. We are renovating the whole space. The beams are actually painted a dark grey, almost black, and the t & g is fir not pine. Rae_gw and Rachel Lee, I would love to see some photos. Paint guy 22, thanks for the tips. I agree I'll have a better sense after priming. Any thoughts on sheen?

Satin.

It took me maybe 2 hours if that long to do the caulking on 3 walls -- I wasn't trying to fill the v-grooves, just fill larger gaps in joints in this 66 year old paneling.

I agree with satin -- I just think painted paneling looks right with a little sheen, but you don't want a really shiny finish on the ceiling. Eggshell even might work -- I stopped using Behr eggshell a few years ago because they changed the formula and it had more of a sheen than I liked on the wall.

I will try to get a good picture. It is a very gloomy day today so hard to get a clear photo of the details.

Tony Stevens -LOL! So true....wish I'd thought of that before I went broke from the rest of the reno! I think I'll paint it and if it's terrible I will get the drywallers back.

Caulking upside down and high up in the air will not be fun. Plus, the caulk can shrink despite what they put on the tube.