A recent and v amusing post by Robert in the Oil forum brought the question of authentic (and toxic) materials to mind. Should we use them knowing they are toxic in the hope that by using 'authentic' materials we will learn something lost in modern equivalents?
Robert makes good the point that 'toxic' is not an equivalent to 'lethal'; and indeed if one uses lead white or vermillion with care there is no reason to assume these paints will have an adverse affect on one's health. The thing is, using the paints carefully is the exact opposite of how they were normally used - look at a Turner or Rembrandt and you'll see a mass of impasto, splashes, rubbing down and (famously) fingerprints.
Now I love my painting, and I'm addicted to historical painting techniques, but put my fingers in a lovely gooey slather of Lead Carbonate, or mercury rich Chinese Vermillion? No thanks.
What one can learn from authentic materials is their working properties, lead plasticises, has a 'ropey' rheology and is siccative for example, so it makes the paint behave differently; so differently in fact that Lucian Freud uses it as his white of choice.
These things matter to experienced painters, but one needs to have a fairly exacting and consistent need for a ropey, siccative, slightly yellow and semi opaque white before straying away from a far less toxic and inexpensive zinc/titanium mix.
Also are modern alternatives really that bad? Not at all; intense modern colours are often far better in saturation.pernanence, toxicity and cost than their historical equivalents. Imagine what Turner might have achieved with pthalos, hansas, napthol scarlets and bright, intense whites.
So my head says paint with modern materials, but in my heart I love the tradition of using lead, boiling linseed oil, making mediums from resins and all that stuff - painting is about the experience of painting as well as what is painted.