Should negatives be printed emulsion side up or down? In this regard, I mean should the light from an enlager be projected thorugh the emulsion or through the back side of a negative?
Also, apart from reversing an image, what differnce does it make if one side, or the another side, of an negative is used for projection printing?
I guess that if you know that printing emulsion side up will reverse the image, then you already know what is standard operationg procedure. "Should" doesn't really enter into it. In theory, if the base is below and not above the focal plane of the emulsion there will be refraction and diffusion issues that otherwise wouldn't be in play. Whether or not you find them noticible or troublesome is your call.