Rings after cutting through coating without prior sanding off of ridges left by planingscraping?

[vestal frigate]

First, I want to point out I'm translating his words, not vouching for them.

The claim is that if your surface is not dead flat and you use varnishes that do not blend in with the previous coat you may be sanding and sand away a high spot of varnish "cutting through" to the previous coat of varnish. When you cut through, the seam between the two coats will be revealed as rings or blobs.

[tight ember]

I concur. I don't know what varnish he is talking about, but think of it like layers of paint.

[vestal frigate]

oh man, that's a great way to visualize it. A layer of red paint under something like green paint. It would be insanely obvious if a high spot made it into the red.

That is correct.

I think Poet and I are both a bit skeptical about these rings being visible, but that's what is being described.

[tight ember]

yup, and the coats of finish will even amplify the minor imperfection on the base

so a little ridge can get pretty large after 4 coats

[vestal frigate]

ah

The "bump" could be any topography.

Imagine a little island hump instead of a clean ridge like that.

You'd have a "trough" or something with this image.

That for sure seems to be what he's talking about. Again, a bit skeptical. 😅

[tight ember]

you're too focused on the shape - just think of it like this

[tacit wedge]

It's super visible with certain film-forming varnishes that are catalyzed or do not burn in at all

Mostly if you're trying to rub it out, it will polish differently and in the gloss angle you will see rings

[vestal frigate]

The shape of the high spot on the wood will create the shape of the "rings".

[tacit wedge]

An onion has a single outer layer, clearly some topography but a smooth continuous out layer. Cut through it on any flat plane, however, and you will reveal layers within it.

Same thing.
Any time you take a varnish down to a flat surface you have the potential to expose lower layers