In the production of solid watercolor paints, stearic acid is often used in combination with the following functional ingredients to optimize overall performance:
Gum Arabic: As the primary binder in traditional watercolor and gouache, gum arabic is fully compatible with stearic acid. In fact, stearic acid improves the rheology during processing, ensuring smoother compression molding and a more uniform, fine surface finish for the paint cakes.
Glycerin or Sorbitol: When used with stearic acid, these humectants precisely control the hardness and re-dissolvability of pigment cakes. Glycerin slows moisture evaporation to prevent cracking, while sorbitol maintains flexibility, ensuring the cake can be quickly activated with water even after long-term storage.
Ox bile or synthetic wetting agent: Ox bile, a traditional wetting agent, significantly improves pigment flow and ensures even spreading. Stearic acid acts primarily as a stabilizer in this system, preventing the wetting agent from separating or migrating during drying. This guarantees natural color transitions and smooth brushstrokes when using the pigment.
In terms of usage, stearic acid is typically added in low concentrations (generally 0.5%–2%). Overuse makes pigment cakes overly hydrophobic, hindering water penetration and forcing users to repeatedly wet the brush just to pick up color, which severely degrades the user experience. Moreover, not all "solid watercolors" contain stearic acid: some modern, budget-friendly solid watercolor products use polyvinyl alcohol (PVA), dextrin, or other synthetic resins as primary binders. These formulations have entirely different requirements for stearic acid—or may exclude it altogether. Therefore, when analyzing or replicating a product, you must determine whether to include stearic acid based on the specific binder type used.
GUIZ Liutong 26-7-2