I've not caught if its been said yet, but one problem with hairspray is that
over time many will severely yellow. Hairspraying drawings and charcoals
was a habit from high school I carried into my college years and many of
them have today a strong yellowed appearance.
Kamar acrylic sprays at Walmart and Kmart stores are not really all that
much more than hairsprays....and for things that might be best to preserve
color such as pastels, I'd consider spending a couple more dollars.