Gouache

 am currently working on a painting in gouache.   I have acrylic gessoed a piece of mountboard - this surface is working well, grabbing hold of the paint.   It can be a problem working over a layer of gouache, as it can be disturbed by a wet layer going on top,   To avoid this problem I sometimes use a fixative spray or an acrylic matt medium  -  you have to wait for this to dry before continuing.