When you count cells, you often mix them with a dilute solution of a dye which is excluded by living cells but can cross the membrane of dead cells — this allows you to count viable and dead cells separately. Probably the most common dye for the purpose (at least, the only one I’ve ever used) is Trypan blue, which is a very pretty blue color.
Everyone has their own ways of adding the dye; I tend to recycle the lid of a discarded culture dish as a mixing surface, pipetting 10 µl of 2X Trypan blue in buffered salt solution onto the lid and then mixing with 10 µl of cell suspension. Since the cell counter only takes 10 µl, that leaves half of each mixture drying in spots all over the lid as I count my way through my cultures.
One day I decided to take some photomicrographs of the resulting patterns. The crystals are salts; I think the dye tends to dry into blobs rather than crystallizing. The round things that look like alien eggs in images 2 and 3 are what was left behind by air bubbles.

I was reminded today, by Björn’s post about modern art, of something I’ve been meaning to post for a long time. I’m hardly the first person to notice that the products and by-products of scientific experiments can be very pretty, and I find that often the story and the science behind the object or image gives it an extra dimension. For instance this:

is electrostatic discharge, captured on x-ray film — static electricity that really is static.
It’s an artifact caused by wrapping developed chemiluminescent western blots in cling wrap prior to exposing them — you have to wrap the blots so as not to wet the film, but it can create static discharges which fan out across your results when you peel the blots away from the film in order to develop it. This is one that was well away from my data, so I scanned it just for itself.
I’m sure I could string together 500 words of postmodern bullshit about the fact that this picture was the accidental result of a real experiment, a (literal) spark thrown from the anvil on which knowledge was being forged… all I need now is an agent with contacts in the art world and a bunch of people with more money than sense.

Update 090709: Ha! I’m in good company, apart from my snotty remarks about the art world of course — about half way through this story, modern master Hiroshi Sugimoto talks about pictures he made in the darkroom without a camera, using static electricity. And yes, they look a lot like my autorads!