I got asked just this week by a learner what was the difference between Ultramarine Blue paint and French Ultramarine Blue?
The short answers is not a great deal. In the early 19th century the cost of ultramarine made from lapis lazuli was much higher than any of the other pigments, so much so that some artists did not use much blue in their work if any.
Two French chemists discovered some blue residue in a soda furnace one day and wondered if this could be developed into a blue paint to replace the costly ultramarine pigment. After lots of development work an alternative was developed which was cheaper and soon came into production. In order to differentiate it from the lapis lazuli it was called ‘French’ Ultramarine.
Today the lapis pigment is still available and but it remains highly expensive so many colour manufacturers use the artificial ‘French’ Ultramarine in their ranges. The lapis pigment is generally no longer used commercially. Today the ‘French’ part of Ultramarine has been dropped and it is rare to see ‘French Ultramarine’ in the shops. Most French Ultramarine paints are now just called ‘Ultramarine’.
If you are ever in doubt of the differences between the two ‘Ultramarine’ and ‘French Ultramarine, generally speaking ‘French Ultramarine’ can have a very slight red shade to it. Ultramarine can sometimes have a slightly greener shade although the differences are very slight.
Ultramarine, French or otherwise is the best-selling shade second only to Titanium White. Ultramarine blue is a good ‘base’ blue for colour mixing as it is a mid-tone blue that is neither too red or green in tint.
Also see my post How can I learn about Colour?