As an aside to the last post about the 1983 Chicago CTA map, Dennis also sent along this fun little “How It’s Made” video about the process used to create signs such as this.

In the case of the CTA signs, the background blue would be the second layer applied to the steel signboard, and white and black would be the two screen printed colours that are then fired and fused permanently to the backing. It’s a time- and labour-intensive way of making signs (largely replaced by full-colour digital printing today) but it’s absolutely fascinating to see the process involved.