Prior to (and during the 'early days of') the current enlightened move towards using only acid-free materials for framing elements , just about anything would/could be used by framers ...a partial list of materials I've personally seen used :
plywood , masonite , pressed-pulp , tin , paneling , dross , cardboard , cardstock , plexiglass , steel , aluminum , hard & softwoods , veneers-on-paper , butcher & brown 'wrapping' paper , starched fabrics , chipboard &/or anything else large enough to do the job .
'Normal' is a tough one for me to define , especially during the earlier era of the art-framing 'world' .
One thing that I've noticed thru the years - some of the lighter/flimsier frames used to have stiffer backings attached , prob. to help add strength to the whole assembly (the backing mat'ls tended to be cheaper than the actual frame moulding mat'ls) .
