I think using student paints for lower layers of a painting is a great way to make your paint budget go further. With reputable brands, their student paints are cheaper than their artist's quality paints because the colors are created from the less expensive pigments. It's the dirt-cheap brands we need to watch out for, where the pigment is stretched with extra filler and binder.
For an expert answer on the the Winton fat-over-lean aspect, I asked Paul Robinson from the Winsor & Newton Technical Team. He said:
As far as Winton and W&N Artists’ Oil Colour are concerned, yes the ratio of oil to pigment is slightly higher in Winton, but only slightly. This isn’t how we achieve the more economical price however. That is achieved through reducing the amount of colours available i.e. dropping some of the more expensive pigments (no Rose Madder in Winton!) whilst still maintaining a balanced palette. There are 120 colours in our Artists’ Oil Colour and 40 colours in Winton. Once the more expensive pigments are removed we look to source alternatives (often hues) or may load a slightly lower amount of the same pigment.
"That said; any increase in oil ratio (as far as Winsor & Newton are concerned) is not sufficient to consider when following the fat over lean rule. Winton is fine in lower layers with Artists’ Oil Colour in upper layers, the two ranges are fully interchangeable and mixable."
So there you have it from a technical expert. Not only can you not worry about using up your student paint in your underpainting, but you could continue to buy student quality for it to make your budget got further.
