Inexpensive 'poster paint' tempera powder blended with silicone grease.
The paint formulation applies to cardstock with brush smoothly.
The paint is dry to the touch in about 1.0 hr at 20 Deg.C.
The dried paint will be inspected over days/weeks with/without topcoat of cellulose ester varnish.
Top: chitosan added to the paint.
Bottom: no chitosan addition.