Binder Medium - is an acrylic emulsion and acts as a sealer to prepare porous surfaces before using gesso. It also provides a somewhat "slippery" ground preparation in its own right. It can be used as a medium when needed to toughen paint for conventional acrylic techniques like scratching back, or as a glue for collage. Gesso Primer - is a flexible acrylic ground with a high grit content, designed to provide a stable white surface on which to paint. Gesso Primer may be used directly from the container for all over thick textural effects. Liquid Gesso Primer - has a thinner consistency, which spreads more easily for a smoother painting surface.