The first photo shows what can happen if a violin is not wiped regularly after playing to remove the rosin residue.

Over time, a crust forms that is bonded to the varnish and can no longer simply be wiped off.

The only solution here is to go to a luthier. He/she can use chemical substances to separate the layers again and restore the original condition. (See 2nd photo).

To prevent this from happening, I recommend always wiping the violin after playing with a microfiber cloth or a commercially available dust cloth, preferably without any cleaning agents.

Wipe the strings and remove any colophonium residue and clean the bridge and hands on the instrument. It is best to use two different cloths and wash them regularly.

Click here for an article on damage caused by care products.