Being a dentist and a pt/pd printer I am very familiar with x-ray duplicating film since we also use it to actually duplicate x-rays. The film I use is Kodak XOmat-2 and process it with Kodak GBX developer and Fixer (water as the stop). The chemistry lasts about a month once it is diluted. Agfa made x-ray duplicating film as well and may still have that in their product line. The film is a reversal film in that chemistry and produces a negative from a negative. It is very simple but the film is very slow and somewhat expensive. Be sure to put the original negative upside down in the negative carrier in your enlarger. You should use a red safelight. The film is notched so the emulsion side is up when the notches are on the upper right corner. Burning yields a "lighter" negative and darker print area and dodging yields a lighter negative and darker print area. It is easy and gives great results.