Quote Originally Posted by ralnphot View Post
Positives were set up in copy cameras and four different negs made using color separation masks.
Half tone screens were also used to create the dot pattern required to produce a range of tones (look closely at a newspaper picture).

Quote Originally Posted by ralnphot View Post
One neg each for cyan, magenta, yellow, and black. The negs were then used to "burn" offset litho plates for four successive printing runs
I didn't know negatives were used for making offset plates. I assumed it was positive like we use for screen printing.

Quote Originally Posted by ralnphot View Post
with a fifth run to add text.
Extra print runs are also sometimes used - known as 'spot colour'. This is where it is desirable to print something in a solid colour rather than make it up from the CMY colours. Also used for exotic colours like gold, silver and bronze.

Steve.