A couple of weeks ago during one of my darkroom sessions, I decided to do an enlargement of a black and white fishing boat photo I had recently taken at Brighton Marina.
I currently use the Ilford Multigrade IV RC De Luxe photographic paper in an 8x10in size since I think this is a great photo paper for beginners and also I can use the Ilford contrast filters on it.
I used a masking frame easel whilst doing the enlargement and in my first print I came across some darkness at the bottom left hand corner of the white border:

I did another print and still had the same problem as in the above photo. I’m always very careful in packing the photographic paper away before putting the white light back on and I thought to myself that it must be a masking frame issue since I had never used this particular masking frame before.
I therefore taped the corner of the masking frame down from where this problem was occurring and was still getting the same black mark.
After several prints and much frustration wondering why the masking frame was not working correctly, I then made this print which ended up being a slightly different black mark to the other prints:

I then began to question whether it was a photographic paper issue after all and not the masking frame as I had initially thought.
Before making these enlargements, I had printed a contact sheet of some beach shots I had taken using my Hasselblad 500 C/M camera as I had recently got the developed film back from my local lab.
I decided to look closely at the the contact sheet and immediately saw the same issue in the corner:

At this point, I knew that it was definitely a paper issue and although I thought I had been careful with not exposing my photographic paper to white light, at some point, I must have not bagged this particular corner of the paper up properly so the whole batch of what was left must have got exposed.
Thankfully all was not lost as I was able to trim down the border to still have a nice print since it wasn’t on the main photo. I was also glad that I found out what the problem was as that was frustrating me the most.
All was not lost with the remaining photographic paper left either as I was able to cut the remainder of it up and use it for test strips.
I’m really hoping I’ll never make this mistake again and I now triple check I’ve wrapped up that photo paper properly before turning on the white light!