I am aware of that John, from my days earning my A&P licenses at Aviation High School. I had to make the posts about the P-51 so I can copy & paste across the fora, one being the P51 SIG who are strict that the content be directly related to the special interest group.
Your memory matches mine; the sheets were red ink stamped on one side and we used to wash it off (not sure with alcohol or some other clear liquid) prior to buffing when they appeared on external surfaces. Internal surfaces were primer coated so they were not removed whenever they appeared on the interior side of the skin. Our teachers would stress grabbing the correct sheet to work on and also trying to get us to have the clean side as the outside. When mistakes occurred, the panel was reused with a different pattern which sometimes necessitated the stamping to be on the external surface.
Thanks for bringing back those 'old school' memories!
Wow, lots changed at the school I attended (then again, it was four decades ago when it was still all boys)!
Aviation High School
I see the school donated my favorite aircraft to the Historic Aircraft Restoration Project (HARP):
Yet, they still seem to have the A-4 Skyhawk that was rescued from the plinth at the base of the Verrazano Narrows Bridge once the military closed bases in the city.
OK, enough nostalgia!
Regards,