I can't see a close-up of the picture (it says you haven't given us access). When did you paint (or how long have you had the house if you didn't paint)?

need better pics

Sorry about that. Hopefully I just fixed it. In the picture, what looks like a dark wet spot is actually dry, and not pulling away from the plaster, but has a crusty surface. I've had the house for almost 4 years, and i didn't paint it. Thanks for your help!

what's on the other side of the wall?

A closet, and there's no damage on the other side. Thanks.

Hi, wgrubb - how long has it been that way? Was it like that at all when you moved in, or - if not - how long ago did it start? Was it a slow, gradual change, over a period of years? Or a sudden change, over a period of months?
Christophern is right - can you post more pics? Maybe a closer detail of the spots, as the original pic will provide a reference as to size & location.

(I'm wondering if the outlet has any relevance to the "rainbow" shape directly above it? Anyone else have any thoughts in that direction?).
Probably not, but it just had me wondering - but I know that sometimes a coincidence is just a coincidence, lol.

Here are some close up pictures...thanks for all your help!

Looks like moisture form some source.

Is the house old enough to have calcimine?

A register and thickly applied latex paint can look like that.

Are the flakes of paint flexible or do they break at the slightest bending?

Also, to answer your question, ks_toolgirl, I'm not sure how long the wall has been like that because my sister was in this room and had the furniture over register. I think it started being like this about 1 1/2 years ago, and it looked like was wet when I first noticed it. Once I moved the furniture peice, it seemed to dry out but got bigger and the spot came to be really dark like it is. It almost looks like there something oozing out of some of the cracks.

Brickeyee-Could it be wet from teh register on the floor? i do think it was wet to begin with but i can't figure out from where.
I'm not sure what calcimine is, but the house was built in 1924. THe flakes break at the slightest touch/bending.
Thanks for your help!

Hmm.. The top image reminds me of the way our wall looked behind our saltwater aquarium, but I'm sure you'd have noticed if she had one.

Could it be some sort of mildew is growing, where moisture got under the outer layer of plaster? (Note - I'm not necessarily talking about "deadly, get your family out of the house, toxic mold"). Is it possible that, as a growing organism, it would spread back under the surface - causing the separation?

Efflorescence?

I probably shouldn't even be offering (admittedly uneducated) opinions, lol. I rarely know what the heck I'm talking about! I hate that I'm always asking for help & advice, but never able to help anyone else. So I thought I should at least give it a shot. :-)

Condensation form a cooling vent could contribute.

Very brittle chips would tend to indicate older alkyd paint and possibly calcimine.

Latex paint is usually at least slightly flexible.

You might leave it open and as is for a few months and see if it stops getting worse before trying to fix it.

Water damage; a pretty good quantity of water is being introduced into that wall from an as-yet-unknown source. Get to know the source.
Casey

Water damage; a pretty good quantity of water is being introduced into that wall from an as-yet-unknown source. Get to know the source.

From here ,I would have to agree.

what is above and below? are there pipes in the wall?