Cracks

I was making another set of three nesting boxes for a birthday present -- this time for my other daughter. The largest box had a hairline crack in one side. After I'd filled the crack, and applied a coat of sealer and three coats of polyurethane, it wasn't very noticeable. The photo shows what happened when I painted the interior with milk paint. 

Wood expands and contracts with variations in moisture content, which is affected by the humidity of the surrounding air -- even when the wood is painted or varnished. Water in the milk paint was rapidly absorbed by the inside surface of the box, causing rapid expansion and stress. A couple of hours later, when the paint had dried, the crack didn't look quite so bad, but it was still very obvious.

The crack in the table is a different story.