Paint Pigment Series
If you've been shopping for paint, you'll notice that intermediate and professional quality paints are priced by series. Student quality paint contains less pigment and is usually priced uniformly for all colors. The series number is based on the cost of the actual pigment that the paint is made from, with paints in Series 1 or 2 costing a fraction of those in Series 8 or 9.
Acrylic, watercolor and oil paints are made out of the same basic pigments, suspended in different binding media. It surprised me to learn that many paint colors are still made with natural, earth derived pigments. Depending on where the pigments come from and how they are processed, some are more costly than others to produce. There are a few synthetic versions of expensive colors, often called "hues," that are much cheaper but perform differently.
Usually the motivation for switching to a synthetic pigment is cost. My favorite paint color, Ultramarine Blue was historically produced from the semiprecious stone lapis lazuli and was very expensive. In the 15th century, it was so expensive that an artist would charge extra on a commission if their client wanted blue in the painting, just to cover the extra material cost. Now that a chemically identical synthetic pigment is available, Ultramarine Blue can be produced cheaply, and is usually Series 2 when you buy it in the store. Other synthetic pigments, such as the Quinacridones, are more expensive to produce, and therefore more expensive to purchase in the store. Another one of my favorite synthetic colors, Quinacridone Crimson, is Series 7, and was developed as a lightfast alternative to the older Alizaron Crimson.
Sometimes, synthetic alternatives are made to replace paints that are hazardous or derived from animals. The beautiful Vermillion Red is very toxic, and has been replaced by synthetics in recent years. Vermillion is still available in artist's paint, but very few artists use it.
Paints with a higher series number are not necessarily better or more lightfast than their Series 1 counterparts. I've noticed that the higher series tend to be more transparent, which gives you more options for glazing, but this is not always true. I'll be posting a section next on how to read paint tubes when buying paint.