I clean a lot of little violins. Our rental program goes down as small as 1/32, and there are six more sizes between that and a full. Every time one comes back to me, either as a return or an exchange for the next size up, I go over the whole thing and touch up any dings and fix anything that needs fixing and give the whole instrument a good cleaning so it's ready for the next person.
Now, on the smaller instruments in particular I've had this recurring problem with stains on the front of the violins. They are always on the treble (right) side on the lower bout, and they run diagonally across the instrument. It looks like someone spilled pop or water on the varnish, and it's hard to remove. It has puzzled me for the longest time because I don't know how or why anyone would be drinking anything while holding their violin, and it happens more often than made sense.
But I finally figured it out.
I was helping Mona practice today. She's working on the Itsy Bitsy Spider, and the bowings in it are a bit complicated. Mona wants my help but doesn't listen. It can get very frustrating for both of us sometimes when the music is hard and she's struggling. On her third time through when I corrected her again about the same spot where she kept getting it wrong, a large tear rolled down her cheek and plopped onto her violin. Onto the front, treble side, lower bout, and it slid diagonally off the edge of the violin.
Those stains are tears. And they don't polish out easily.