Velatura. I love this word, it just rolls off the tongue, Veeelllllatuuuuuuraaaa.. Velatura is somewhere in between a glaze and a scumble. It is a thin, milky glaze that is semi-transparent and acts like a veil somewhat obscuring detail when it is applied. A scumble is more opaque and is rubbed over the surface, or dragged across a surface which only reveals the underpainting due to the texture of the painting. A velatura completely covers the surface and is juicier than a scumble due to the amount of medium in it. I often use velaturas, any opaque paint will become semi-transparent when you add enough medium to it-- thus becoming a velatura. I often use this type of application in landscapes, they create beautiful atmosphere.