Old violins often have pinholes in the varnish. No one knows exactly how they got there, but they imply some things about how makers 300 years ago varnished, and what was important to them (pinholes obviously didn’t bother them much). This probably wouldn’t happen if the wood under the varnish was too well sealed, except we can see that sealer is there and that it has prevented the varnish from going into the wood, and pinholes aren’t compatible with that. It’s one of those little mysteries.
The violin in the photo is a very early G.B. Guadagnini from Piacenza, with bright red varnish. The size of the area in the photo is probably about 12mm across.