Aircraft cutaway drawing on a sheet of anodized aluminum

A. Hi Charles.

A long long time ago (in a galaxy far far away), blueprints were actually dark blue paper with white lines. They were out of favor by the time I entered the engineering business 45 years ago, but I remember some old timers calling the newer diazo prints -- the ones with dark blue lines on white paper -- "white prints" or "blue lines" to distinguish them from the former cyanotype technology with the reverse colors.

So you have aroused my curiousity to the possibility that the drawing you are speaking of may actually have been a cyanotype "blueprint" done on aluminum instead of on paper. Hopefully someone will have seen a similar drawing on aluminum and will enlighten us what it's about.

Regards,

A. Hi Charles
The F15 entered service in the early 70s which was about when I was involved in resist technology.
There are many variants on the process but it starts with a sheet of aluminium, sulfuric anodise and dye blue (the anodising absorbs the dye) but do not seal. Then print - either screen print or photoresist) a clear lacquer over the part you want to stay blue and either bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon] the exposed dye area or leach out the dye in plain water before the anodised layer has time to seal itself. The process was sometimes used to make aluminium labels etc but was time consuming and expensive. The print you had was probably someone tinkering about in the lab!
There is a way of producing multi-coloured prints which involves filling the unsealed anodised layer with methyl cellulose (wallpaper paste)to prevent it sealing and dyeing through successive resist images. Very tedious and expensive but made lovely full colour prints.

A. Thank you for your responses.The information jogged my memory and I recall my Dad explaining the resist process. My Dad was a Line Chief with the 1st Tactical Fighter Wing in the Air Force and was the first combat operational wing to have the then new F-15, This anodized aluminum drawing was just one of many F-15 memorabilia that the McDonnell Douglas Service Reps gave to my Dad.