There are many misconceptions about historical pigments and their relative toxicity, compatibility, lightfastness, and consistency in oil paint. At Natural Pigments, we try to clarify the issues and educate artists as to the facts about historical pigments through the extensive product information found on the Natural Pigments website.
Of the total colors among Rublev Colours Artist Oils (manufactured by Natural Pigments in the United States), only 12 colors have lightfastness ratings less than I as established in ASTM D 4302, "Standard Specification for Artists' Oil, Resin-Oil, and Alkyd Paints." Of these 12 colors, less than half have any compatibility issues, and these are identified on the Natural Pigments website and in the print catalog.
Besides the colors that contain lead white (basic lead carbonate), only nine artists' oils contain pigments that are considered to be composed of "toxic" chemical substances.
The differences between Rublev Colours Artists' Oils and other artists' oils go beyond the fact that Natural Pigments uses historical and earth pigments in oil colors. Rublev Colours are not made with modern additives, so their consistency is quite different from other artists' oils, giving most Rublev Colours oil colors a "long" consistency that brushes easily in the direction of the brush stroke, just like handmade paints without stearates and other additives behave.
Regarding what some have said about Rublev Colors Artist Oils, they most likely have the consistency you are looking for — paint that is "long and flowing." However, since nothing is added to Rublev Colours Artist Oils to mitigate the behavior of pigments in oil (as in some other brands of oils), some colors will not be "long and flowing."