Oiling out – is when you paint a very thin coat of medium over the painting to bring the colours back to how they looked when you first painted them.

Depending on the absorbency of the canvas, the oil can soak into the canvas leaving the paint looking dull. This is called 'sinking- in'. Oiling out can be used to blend wet layers into the layer below but is often best used when you've had a bit of practice with oils.

It is most notable in dark areas of painting, and oiling out enables you to judge the colours as they were when you first painted them. I don't usually recommend it for absolute beginners as you can get into a mess quite quickly and it can create issues with fat-over-lean principles. However, for more advanced painters, especially realist painters, it can be an invaluable technique to use.