What can I do to this ceiling to fill in gaps between boards?

Can you hang a pretty sheet/sheets from corner to corner to hide the ceiling. Kinda a draped effect?

Check with a home improvement store to see if you can take sheet rock Puddy to fill the cracks. You might can do that making a decorative design so you wouldn't have to go back and sand. They may be able to give you some more ideas. Good luck with your project.

Hometalk has featured several articles on the faux metal tiles (made of styrofoam) as affordable ceiling cover. You might check those out.

There are wood filler products out there. Try Home Depot or Lowe’s hey might be able to help you out on suggestions.

I used FLEX ALL

I bought the faux glazed copper on Amazon, super easy to apply and their really pretty, not to expensive either! They come in really large sized so a few go along way!

Are the cracks letting in draft or light? If not,why not just embrace it as the character of an old ceiling, and give it a fresh coat of paint.

Is this just used for storage? If so, look into the 4ft x 8ft panels of styrofoam insulation (I know they have this at Lowes). It has a metallic side and a white side, but could be glued directly onto the boards. It would not only stop the soot from falling onto to your 'tresures', but will help insulate which will help to preserve them also.

Oh dear that's not good. If you can get into the attic you can use expanding spray foam to seal the big gaps.

Hello Judy, hope these help you out.

https://www.hometalk.com/posts/floors-ceilings/dress-up-your-ceilings-with-faux-tin-ceiling-tiles-40995914

https://www.hometalk.com/posts/floors-ceilings/super-easy-diy-faux-tin-ceiling-5930744

Put tongue and groove flooring on the ceiling to add some wood warmth and interest.

That make large sheets of beadboard. I would cover the ceiling in that.