Based on a sketch of a still life, set up by a friend of mine.
Today, 10 days later, I tried to varnish it using a gloss acrylic varnish and a large flat brush.
And now I am sad.
The varnish has dissolved the inks and caused all the colours to mix together and turn muddy.
It might be possible to get away with using a spray varnish (I haven't tried it) but please please please don't use a brush!
Meanwhile, I'll give this one a few days, remove the varnish (using varnish remover), re-gesso the canvas and start again with a more durable medium.