That's also the only thing I could think of. One method of producing positives from positives is to overexpose to the point where the silver halide grains "do a 180°". That's oversimplified for such a complex reaction, but I believe that's kinda how it works. There is a discussion on this topic somewhere...
If you've found a way to get a direct positive from mammography film, that might be a very interesting technique to exploit!
Thanks to all for the comments. It seems I should patent my process as I have found a way to create a direct positive from a positive print! Yes it is due to HORRIBLE overexposure, I had stupidly assume that since I was trying to penetrate fiber base paper that I would need mega-light....wrong! I ended using my D@ with cold lite stopped down to F32! at about 80cm for 4 sec, when using the 300w bulb I was giving 40sec! What was i thinking? anyway all is well that ends well. BTW mammo x-ray film is single emulsion very fast(blue/green sensitive) and has great sharpness abiet a blue base that doesn't seem to affect anything. I develope it in Ilford PQ paper developer for about 2 min. It does require at least a 1 minute presoak as the heavy anti-halation coating interferes with developement. I get this stuff for free from some of my customers as everyone is switching to digital imaging.
No escaping it!
I must step on fallen leaves
to take this path