mattmedium
Mattmedium is a term used to refer to matte medium, a clear, water-based acrylic polymer emulsion added to or applied over acrylic paints to create a flat, non-gloss finish. It is used by artists to alter surface texture, reduce shine, and control how light interacts with a painting. Matte medium can also extend paint, increase flow, and help unify the surface when working with multiple layers or mixed media.
In practice, matte medium is mixed with acrylic color or applied as a glaze, wash, or adhesive
Differences from varnish are notable: matte medium is generally incorporated into or laid down during the painting
Safety and storage are typical of water-based acrylic products: store sealed, away from extreme heat, and use