Argh! Strange Fogging of prints!

[arigram]

After finally been able to find an enlarging frame to do 30x40cm prints, I was shocked that all my first attempts where spoiled by a creeping fog!
The fog is really evident even in the safe lights at the edges where it starts, "creeps" a bit towards the inside and the rest of the paper has wave fog marks here and there.
- I thought it was the safe lights. They were not. I tried printing without any of them (regular smal AP and Kaiser with red/orange filters, at safe distances) on in film tank loading conditions.
- Maybe my new frame bounced the light? Nope. It is a high quality brand new LPL mask with black blades and dark ochre base.
- The white walls? Nah. They are black around the enlarger and the effect of bounced light would not be so severe.
- The trays? Brand new, 40x50. I thought of the labeling on the inside by a permanent marker, but I don't think it is that strong.
- The paper? I tried my "older" 20x25 and 13x18 Ilford MGIV RC papers and all of them developed fog, even though my older prints (made in smaller 25x30 trays) were all fine. The fog was less for some reason in smaller sizes.
- The enlarger? I developed two pieces of paper without light, a 30x40 and 13x18 and both showed fog.
- The chemicals? All of them around 20C, Ilford MG dev, Ilfostop and Rapid Fixer and proper dillutions. I haven't tried dumping them and remixing to see if I made a mistake there because they are 2L each (great waste) but that could be it.

Guys and gals, do you have any clues to help this poor man?

 

[rogueish]

How are these stored? Heat can affect paper. A fellow student had a similar problem, the entire pack was affected.
Did someone open the paper pack under the "wrong" lights? If the light wasn't intense it would fog the edges and reflection could cause the "fog waves".
Do you store your paper in the darkroom with chemicals? I've read that long exposures to photo chems can affect the paper.
Hope you get it figured out and easily solve this mystery.

 

[arigram]

Rogueish, all my papers are stored under the enlarger but I never had similar problems in the two years I have my darkroom. Even though we have a very unsual weather this autumn/winter of about 20C the chemicals and papers have survived two summers of high 30s. Since I am the only one who uses the darkroom and has keys for it, I doubt someone else messed with it.
I'll probably throw away the developer and remix it to be sure.
(I forgot to add that I use distilled water for all my chemicals)

 

[titrisol]

cut a strip of paper and try again with your smaller eassel/frame to determine if that maybe the culprit

if the fog/gray is wavy it sounds like a developer issue

 

[Ed Sukach]

If this fog starts at the edges of the paper and progresses inward, I would suspect some sort of chemical contamination, migrating through the internal base from the edges of the RC paper, where they are not protected by a polyethylene coating. Possibly humidity ... but I would look to something stronger. A thought ... I read an article some time ago, where a gallery was experiencing image degradation on all of its photographs ... and those on RC papers exhibited some migration from the edges - as a result of painting the walls with oil-based paints... "outgassing" of phenols ..? Maybe something similar?

 

[arigram]

As a note, it was the developer.
Something that I overlooked was that I use an old metallic pan filled with hot water that I lay on the tray to bring the temperature up and its bottom had some sort of plaster or white paint left from the darkroom renovation. That must have been the source of the contamination.
It also gave me the oppotunity to try out Agfa's Neutol WA which I found very surprisingly in my local photographic bulk store. I never seen it before, must be a miracle!
Everthing's back to normal now, thank you for the interest and the hands of help you extended.