[Guest]

 

My camera has horizontal shutters, i.e. the shutter curtains move horizontally.

 

Well, it might be then that there is a failure in the shutter above 1/1000 - this could explain the shading on one side.

 

Simple test - shoot a plain wall above 1/1000 and see how the film looks like.

 

 

I will glue the negtive on a clean window with tapes

 

Window light is likely to change - and quite quickly sometimes. Better is to have a consistent back-light (a light table)

 

But you might not need to go through all the trouble. You can investigate the shutter issue first.