Paper glop is pulp for making paper in bulk: one pressed at the Paper Press gives 20 Clean Paper (30 with the Paper Maker perk), with Book writing mastery 2. You mix it at the Formulation Bench from a Water and 12 Flax, 3 at a time, or from a Water and 12 Wheat, which makes only 1. Both need Anatomy mastery 2. Both recipes come with Paper Press (50 red, 10 blue).
The town Alchemist sells 20 a week at every tier, for 25 copper each.