Quote Originally Posted by Born2Late View Post
Blue line prints replaced classic blue prints probably 45 or more years ago. Blue line prints produce a positive image - blue lines with a white backgroung. The blue line prints utilize the diazo process. The paper is purchased precoated. While it is light sensitve, it rquires a very intense light source. As stated earlier, it uses ammonia as the developing agent. There is no fixing required and image is not very permanent.

I remember running a diazo engineering drawing copy machine in an engineering office the summer before my senior year in high school. That would be about 57 years ago. The worse part of the job was pouring the ammonia solution into the machine once or twice a day. I believe later machines took the ammonia out of a container with no pouring.