On Wed, 05 Aug 2020 10:00:52 +0100, Scott wrote:

However, even after about four coats, the topcoat remains uneven. I
can think of two possible explanations:

Brush marks with most gloss paint are almost inevitable. The only
paint I've used that flattened itself well was one of the "one coat"
ones(*).

1. To try to do the job with only one brush, I used a 12 mm brush. I
think the paint may be drying too quickly to allow me to achieve an
even finish.

How wide/long is the shelf? Anything bigger than A4 and your not
going to be able to get enough paint on thick/fast enough for it to
"self level". Gloss painting is a bit like plastering (without the
polishing stage), Whack it on, spread it out to stop runs, couple of
strokes to smooth over and LEAVE IT ALONE.

(*) Possibly becasue it covered so well I followed the above better
than I normally do, particulary the leaving it alone.

--
Cheers
Dave.