First of all, it was great to see you all on Wednesday! The subject of mediums came up a few times and so I'll share what I know about their use. I use a medium to improve the flow of the oil paint that I find a little stiff for my painting so any oil painting medium which says "flow improver" would do this. ( I put a couple of links on the suggested materials sheet).
You can just use a low odour artist paint solvent on its own if you don't mind your paintings coming out quite matt and they will dry quicker. Artist's refined linseed oil (generally what pigments are mixed with in oil paint) makes the painting glossy and slows drying. Many oil painters choose to buy a paint solvent such as zest it or W & N Sansodor and refined linseed oil and mix them together as a medium so as to combine these properties.
I generally pour equal measures into a glass jar and shake it vigorously before use. As I'm only dipping my brush in occasionally I don't use much. You might have to pull off excess paint with a rag before dipping but any residue will settle and so you can just keep topping up the same jar.
Moving on, please don't forget your three tasks which were to bring in a cardboard egg box, a small container of interesting shape but not too multicoloured if possible and finally research the term "Colour constancy"
The egg box starter exercise appealed to me so I gave it a go and got sucked in to the process.
Although the painting became more detailed it lost some of its dramatic impact, but I did learn a lot!
The name of the book I recommended for left/right brain drawing exercises is "Drawing on the right side of the brain" by Betty Edwards. Although it deals mainly with shapes the ideas are very relevant to ideas around colour constancy.
I'm looking forward to Wednesday and hope you are too.