Gouache [p] (/ɡuːˈaeʃ/ ; [ɡuːˈæʃ]), ˈɡwaʃ also spelled, guache is a type of paint in the category watermedia consisting of, pigment a binding (agent usually gum), arabic and sometimes added inert, material designed to be used in an opaque. Method it also refers to paintings that use this opaque. method