I tend to use oil and pigment sticks when I'm starting a painting to get some initial marks down on the paper but they can also be used to work into a painting. The painting does need to be somewhat dry in order to transfer your marks and ensure you are not just moving paint about.
I'm a big fan of oil and pigment sticks especially the R&F ones which glide beautifully onto the paper, boards etc. They refer to them as "lipstick soft" on their website and I'd say that is a pretty good description of them.
They come in a range of colours and have a wonderful transparency to them. The larger sizes come in a tube which is perfect for preserving them and all your other colours as they would generally make quite a mess of everything else... basically like leaving your lipstick in your bag without it's lid on!
They are very different to the oil sticks I've used before such as Winsor and Newton or Sennelier ones which are "stiffer". These sticks have a skin on them, like traditional oil paint does when it starts to dry which you need to peel off to get to the soft oil.
The differences in these sticks can be explained by their composition. With the Sennelier and Winsor and Newton oil sticks a proportion of the oil is substituted for mineral wax.
The pigment stick however, uses beeswax and plant wax which reduces the amount of wax needed and results in softer consistency.
Here is an example of using two different types of oil sticks / bars. The one on the right is the stiffer type of oil stick from Sennelier. The one on the left is a R&F pigment stick.
Using a cloth to smudge the marks you can see the pigment stick on the left spreads and you start to lose the definition of the marks, whereas the Sennelier oil stick on the right maintains its form.
I recently bought this test pack of Sennelier oil sticks for my workshops so that participants get the opportunity to have a go themselves and experiment with their paintings. Oil sticks/bars can be quite pricey so this test pack is perfect for experimenting with.
I bought this pack from Jackson's art supplies for around £9. This is compared to the full sized individual Sennelier sticks between £5-7 each. Prices vary depending on pigment. The R&F oil bars are more expensive starting at around £12 and increasing up to £30+. Again this is dependent on the pigment.
Happy experimenting people!