What is a medium, can they really predict the future...
Sorry not that kind of medium, a medium in this context is a vehicle for the paint, a substance or blend of substances which alter the way the paint behaves.
For example to thin it, or thicken it, to make it dry quicker or slower, to make it paint 'longer' or to build up the layers of a painting in a way which will make the painting last and not crack or change in colour.
In watercolour painting the medium is water, however with oil paints as the name suggests the paint is made from oil and pigment and there are a wide variety of products to change this amalgamation of oil and pigment.
The most basic is to add oil maybe linseed which will increase the gloss and drying time, however now there has been an increase in the use of chemistry to really push this area to a new level and one of our suppliers Rublev really are pushing the boundaries here, making the mediums a real, holistic extension of the paint.