"Shadowing" in easel corners?

Occasionally I notice darkening in the corners of prints. This usually appears when there is a lightish tone (such as sky) in that area.

It doesn't happen all the time, and is usually just in the corners, in fact usually just one corner.

I had put it down to safelight fogging. But I just did a safelight test, with two coins on a piece of paper for five minutes, and there was no image at all, so that seems to be ruled out.

Any other possible causes?

Thanks,
Kevin

Condenser enlarger? If so, possibly the condensers are not adjusted correctly.

What lens for what negative size? Lens coverage may be an issue.

Just putting coins on paper for 5 mins is not really a sufficient test. You need to pre-fog the paper to a level that gives a JUST slight grey tint when you develop it. This avoids the situation where you get a fogging exposure to the paper that does not reach the toe of the paper's curve on its own but will show when the exposure is moved beyond the toe by the normal print exposure.

Tape a coin or similar over the pre-fogged (but not developed) paper and keep it on the enlarger baseboard while you switch on the enlarger with a cap over the lens (this checks light leakage around the enlarger). Keep it there for as long as the longest exposure time you use, plus 50%.

Move the paper to the developer tray position (do not immerse it) leave it there for 150% of your developing time. Move it to the stop tray position for 150% of your stop time (don't forget any drainage time) - you can probably ignore the fixer position as the paper will be sufficiently fixed in 30 seconds or so.

Switch off all lights and un-tape the coin. Now develop & stop in total darkness and you can put the safelight back on after 30 secs in the fix. There should be a uniform slight tint with no sign of the coin's shadow.


Cheers, Bob.

Easel reflections? Happens to me occasionally, particularly with light sky when I'm printing all the way out to the corner of the negative. The strong light from the rebate is reflected onto the paper by the easel if I'm not very careful setting the masking blades.

Sounds possibly like either the light source is not covering the negative or the lens isn't fully covering. Does it happen at all size enlargements or only at larger magnifications (i.e., when the lens is closer to the negative)? If it happens only at larger magnifications or is more pronounced then, I would suspect a lens coverage issue. If it happens equally for all magnificatons then take a look to make sure your light source is covering adequately.

This happens all the time at the negative stage, If you are using negative holders look carefuly with the negative in place. you should see bare metal that is reflecting down on your print. Try lamp black on the inside of both top and bottom plate, not where the negative sits but the chiseled edge. Otherwise look for white cards or something on the enlarger coloumn that is reflecting light.
You see this problem with skys and in portrature with nuetral grey backgrounds

This may seem a little dumb after all these tech answers, but I've seen it happen. To me and a few other fellow students.
Do you use an under the lens filter holder? The kind that is attached using a swing arm, so you can move it out of the way while adjusting lens settings. Check to make sure it's centered. If you don't have/use one than feel free to ignore this post.

Just realized you said darkening not brightening of the corners. The filter holder will block light, not add. Smack me upside the head and say "think about it".
Sorry, having a Simpson's moment.

Kevin
I read your post too quickly and answered two quickly.
It is possible that you have a hot spot in the mixing box!
It is possible that a shiny surface is reflecting into the corner area.
It is possible that an object, canned air or white card near the easal is reflecting onto your print
Also check your enlarger with your head on the easal and look up while the enlarger is on, you may have a light leak that you can not see when standing in front of the enlarger.
when the negative holder is filed back and not matt black painted (where you file) you will get a plus density line in open areas, and that is what I quickly thought I read.
Is there a Led light in the room that is casting a shawdow, Radio, humidifier??
This is a tricky problem.
Try making a print to nuetral grey with out the negative in place. Any defaults or uneveness will show itself.
good luck

Thanks all for your replies. It looks like I'll have to investigate it further. Definitely seems to be some kind of reflection. And I think it mainly occurs not at large enlargements but at small enlargements. Anyway, thanks again, and I'll check your suggestions.