This is a minor piece of repair work. I do not want to put more than one more coat on the background. Ideally, I will put no more on. However, I let a brush stroke feather out too far, and there was a touch of pale paint on the dark background.

I rubbed it out with white spirit, and this gap in the paint is the result. The background was not yet entirely dry, and it just came off on the cloth. It is better to repair these things early than to leave them until later and risk a repair not being in the same spirit as the rest.

I went over it with the dark blue mix, rubbing the edges with my finger to make the paint as thin as possible, so that the patched area would blend in when it was as dry as the under part. You can see that a lot of paint had to extend downwards from the true patch, to be certain that it would look good on the darker shadows. This is, by the way, one reason why we use varnish. It pulls together different consistencies of oil which will be there on the canvas because of how oil dries over the course of years. Different pigments will have different amounts of shiny. Varnish makes the whole painting equally shiny or matt.