Always lay your oil paints out on your palette in the same order so that, with time, you'll be able to pick up a bit of a colour instinctively.
The proportion of oil (medium) should be increased for each subsequent layer in an oil painting – known as painting 'fat over lean' – because the lower layers absorb oil from the layers on top of them. If the upper layers dry faster than the lower ones, they can crack.
Avoid using Ivory Black for an underpainting or sketching as it dries much slower than other oil paints.
Pigments containing lead, cobalt, and manganese accelerate drying. They can be mixed with other colours to speed up drying and are ideal for under layers. (Student-quality paints usually contain cheaper alternatives to these pigments, generally labelled hues.)
Use linseed oil for an underpainting or in the bottom layers of any oil painting done wet-on-dry as it dries the most thoroughly of all the oils used as mediums.
Avoid using linseed oil as a medium in whites and blues as it has a marked tendency to yellow, which is most notable with light colours. Poppy oil is recommended for light colours as it has the least tendency to yellow (although it does dry slower).
Don't dry your oil paintings in the dark. This may cause a thin film of oil to rise to the surface, yellowing it. (This can be removed by exposure to bright daylight.)
If, as the paint on your palette dries it forms a lot of wrinkles, too much oil (medium) has been added.
If you're not sure whether a bottle of mineral or white spirits is suitable for oil painting, put a tiny quantity on a piece of paper and let it evaporate. If it evaporates without leaving any residue, stain, or smell, it should be fine.
If you want to clean away a layer of oil paint or oil varnish, use alcohol, which is a powerful solvent.
Tip 11: Remember that you can paint with oils without using solvents, using brush pressure to spread the paint out thinly, only oil as a medium and to rinse your brush.