Altered Art Projects -> 
Seal & Envelope Mucilage

6 tbsp pure white vinegar
4 packets (1 oz) unflavored gelatin
1 tbsp lemon extract

bring vinegar to a boil, add gelatin and stir until dissolved. add lemon, mix

make 1/2 c

brush on, let dry, then lick to seal.
make your own stationary
store in capped bottle for several months. remelt in pan of warm water