I have another problem with my varnish. It's laying flat now that I remove the shine before putting on the next coat but the problem I now have is that I always get small bubbles in the varnish that don't disappear and when the varnish is dry, and the surface is marred by these bubbles.

It seems that the bubbles are caused by my using a paint brush to apply the varnish. No matter how careful you are, if you use a paint brush you are likely to get these small bubbles forming. The reason, so it seems, is that a paint brush is designed for, well, paint. The bristles are fewer and thicker than you should use for varnish and as a result air is easily trapped in the bristles when you load the brush with varnish and transferred to the varnish when you brush it on the surface. Paint, being thicker, doesn't suffer the problem.

So what should I do?

One good way to get a fine varnish finish is to apply it with a 4" foam roller fairly quickly and rolled well to ensure that the varnish is well distributed and then, before the varnish starts to harden, tip it off with a very fine brush to remove the bubbles which will be plentiful due to the foam. Badger hair bristles are suppose to be the best for this so I have bought two fine brushes, one synthetic and the other badger hair and I have to tell you, a badger hair brush is expensive.

It also means that instead of throwing away the brush after use I shall have to clean it but since the brush is for tipping off and not application, it should be easy to do.

I hope.

I'm not going to be able to get a very fine finish since I am either varnishing outside or in the workshop and it would be a great deal of trouble to build a dust-free environment in either pace. So I'll no doubt have dust and possibly even small insects in the finish, but hopefully no bubbles.

[Edit 2020.10.08]

I have received my two new brushes and decided to give one of them a try. I applied the varnish with a paint brush, just slopped it on any old how, then I used 4" foam roller to roll over the varnish a number of times to even out the coat. This put lots of bubbles in the varnish. Then I used the synthetic brush to tip off the coat and lo and behold, no bubbles

There's still dust and insects getting on the varnish but no bubbles.

Deep joy !