I have been experimenting with grounds for about a year. I have been using the settled pigments from my Gamsol recycling can, tinted or shaded, warmed or cooled, and mixed with walnut oil and Gamsol. This gives me an oil primed surface. I love how the darker grounds make the high values and intense colors jump off the canvas and being able to leave a lot of unpainted surface is appealing to my eye. Over time the grounds have gotten darker. Cool seems to work better indoors and warm does well for landscapes.