Only thing I would add is to use 400 speed film. I thought with 100 speed film I experienced a threshold effect that kept density from building in the way I had hoped. With 400 speed I did not experience this.
Originally Posted by NB23
Geez guys the guy is only asking a simple question.
To the OP: Just put the camera on a tripod, set the camera on B, choose f4 or f5.6 to start with. Use a soft-release with a lock capability.
Click the shutter and keep it open for an hour.
Then Two, just to have a more pronounced effect.
And then 3 or 4 hours, if you have the time to do so.