From my days in the 80's and early 90's...
Originally Posted by Chrisk99
Positives were used so that the proof which was either a chromalin (kind of like a dye transfer) or a colour key (four coloured, CMYK tranies registered to create a colour composite ) could be matched and adjusted to the the original positive. The positive could also be used to do a press proof but not for a magazine (unless you bought a whole bunch of pages). Postives were wanted because it was a good 'go by', and was the source of the separations. Positives were also preferred because there is too much scale (the best printed page in a mag is probably 3 or 4 stops and a good neg can have 11 or more), far too much variance in interpreting a neg and separating a neg to match a print is painful (making a separation from a print is easier, but the quality is substantially lower).
Again this is back in the day, but...
Originally Posted by Steve Smith
Web presses intended for full colour printing will have 4 or 5 heads/towers and may have the same on the bottom so that the mag gets printed front and back complete in one pass. Spot colour for a magazine is generally done by mixing CMYk, unless they are having a special on a specific colour like a metalic.