Red Lead, also called Minium or Surik. Very poisonous. This color was popular historically, but is now more-or-less obsolete. Rublev carries this as an oil paint, and it is one of the few paints of theirs to contain an additive as it has a short shelf life (as in maybe several months) when made into oil paint, and the additive will extend the viability of the paint a bit.
This color is very toxic (Natural Pigments says to use utmost care to avoid exposures to this pigment- see their site for more details and as always be sure to do your own third party research). The dry pigment is reported to be surprisingly reactive, and light may blacken it. However it does seem that binding it in oil may have some sort of protective effect. Even in oil it may have some sensitivities to the environment and may also perform poorly in mixes, though we have not verified this.
More information on hazards from lead pigments can be found in the Artist's Guide to Health and Safety. Author Monona Rossol has updated work which can be found through her site.
