Winsor and Newtor oil paints - different series?

[Zapp!]

I was getting some oil paints yesterday and I saw that there are different series of colours within the same range of Winsor and Newton oil paints. So for example in their Artists' oil colour range there are some colours which are series 1 and others which are series 4. But there is a huge price difference between these with a 200ml series 1 tube costing about £25 and the same sized series 4 was about £50.

I was wondering if anyone could please explain to me what makes some colours like Cadmium Red or Viridian (which are series 4) double the price of Titanium White (series 1) ?

[Craig D]

The cost of the raw materials. If a pigment is cheap to obtain and/or produce it will be in series 1 etc.

They group them into series so that smaller price differences don't mean that every tube has a different price.

[Zapp!]

Ahh, that makes sense. Thanks very much.