What kind of easel are you using? I vote for the easel. I have seen this before with single size easels that use a heavy matt black hinged metal frame to hold the paper down. When closed, this creates a "wall" about 5mm high around the print. Even though the metal is flat/matt black, it will reflect light back down onto the paper creating an edge of slightly higher density.
The effect is variable depending on how much density is in the negative in the part of the image being projected onto the inside edge of the black frame in the easel, so if one is printing full frame, the intensity of light hitting the inner edge of that black frame can be quite high since it is only coming through base fog negative density. In your example you have the "perfect storm" scenario for making this effect visible - ie lots of light hitting the inner edge of the easel frame, being reflected down onto the edge of the print which has received relatively little image exposure (ie bright sky). So the overall effect is non-image fogging of the high value along that edge.
It could conceivably be reflection from the edges of the glass in the carrier but I still think it's the easel. You could test to see if it is the carrier by rotating the easel a little so it is not square with the negative carrier. Then make a print. If the shadows are square with the negative carrier, it is the carrier, if on the other hand the shadows are still square with the edges of the easel, it's the easel.
Last edited by Michael R 1974; 03-24-2012 at 10:52 PM. Click to view previous post history.