The first varnish coat was dry and hard, so this afternoon I decided that I could do a second coat before leaving for a few weeks of paid work. I lightly sanded with 400 grit paper, followed by 600 grit. The resulting surfaces are very smooth. The varnish went on very easily, but looked very pale. It turned out that the black colour had largely settled to the bottom, and my shaking the jar didn't mix it very well. Next time I will have to stir and shake, and possibly strain the result before using it. I may also add more colour.