I'm no longer confused, it's the Sabatier Effect! Solarization is "The exposure necessary to produce true solarization is in the range of 1,000 to 10,000 times that necessary to produce total black in the negative" (From unblingkingeye.com). What I'm talking about is Pseudo-Solarization.

Thank you PE for thee tip on graded paper, I had a try today in the darkroom, and used some old paper that I had, Ilfospeed Grade 4. I also tried Ilford MG, but the Ilfospeed worked a lot better, it produced good results, the MG just turned out more or less as an over-pre-flashed paper.

Anyone tried with film? Im thinking large format in trays might work, but of course, that takes more time.