The only information I can find about lead is again in Glafkides. p.318.
"Lead and thallium reduce sensitivity and increase fog. Thallium was disclosed by Schwarz in 1926. Mueller stated in 1935 that lead and thallium salts added in a concentration on 0.04 molecules per cent of the silver halide increase the sensitivity of gold-sensitized X-ray emulsions of 50-100%. The addition is preferably made before precipitation."
re lith paper: At one time, I thought lith printers would be a natural cohort of d.i.y. emulsion makers. If I were a lith printer, I'd definitely keep and use my cadmium. But, I think I won't be R&D'ing many new emulsion recipes just for the sake of R&D. There just isn't the interest to justify the time. (Fortunately, it hasn't been expensive research!) Time for this girl to leave her lab-rat comfort zone and get back out into the world and try to "make good art." There really is a ridiculous amount of how-to information on the Light Farm already. It's good info and you can't beat the price!