Edit: on a happier note. I LOVE it when people do things like this:
I like it when people do nice things for me. I do. But for the love of god.. if you are not an artist and you get the urge to clean up an artist's desk.. follow a few little tips.
do NOT under any circumstances, put their paint brushes.. brush tip down in the containers. This bends and breaks the bristles and renders the brushes useless for the artist. Considering how bloody expensive good brushes are, you might cost someone quite a pretty penny. As well as make them unable to do any work till they're replaced.
do NOT stick their inking pen upright in the brush container. It goes in it's own 'omfg sharp stuff' container. It kind of hurts to reach for a brush and get stabbed by your own pen.
do NOT clean off their palette. I know it looks like a messy pile of squished paint all over. But in the case of watercolor artists, that is *reusable*. not trash! And since the high end watercolors go for 15-30 dollars a bottle.. well let's say we learn to be frugal with our watercolor use. Plus I have a memory problem and can't for the love of god remember my color scheme for my current paintings unless I look at my palette.
do NOT throw away some weird paper that looks like a heavy duty white tissue. That's transfer paper. I need it.
do NOT go 'oh this colored pencil is just a stump' and throw it away. Yes it's a stump. I can still use it. Chances are I'll use it till it's DEAD. And if it's black or indigo or dark umber, chances are it's the only one I have left! And no money to get more so.. don't! omfg don't!
Basically.. don't throw anything away. You don't know what it is, and it might be something really important. Watch how you put the tools of the trade away.
maybe in the end the best advice is.. just don't touch an artist's desk. Seriously.
*grumps and goes to fix brushes and dig through the trash for art supplies*