Not arguing here, just trying to understand. Water, in liquid phase, exerts a vapor pressure -- continually evaporating liquid into gas unless the air has reached saturation due to humidity or temperature. It need not be boiled to change over to gas. At any point in time, some small percentage of those molecules will exceed the average temp, releasing water into the air. When the vapor pressure = the atmospheric pressure, that's when boiling occurs.Read up on the scientific definition of vaporization. It's the phase change from liquid to gas, boiling is the colloquial term for the phase change. Using water as an example, the input of heat to ice, solid water, well cause the temperature to rise to the point when a phase change will occur, ie to liquid. To get to the next phase change, much more heat will be required till we reach 212F at STP (Standard, Temperature and Pressure at sea level). So water isn't transitioning till then. Similar thing with lead except the molecular bonds are stronger and lead is isotopically far, far heavier.
With basic science in mind, what you may see coming from the pot is from the impurities, not lead but still not healthy. In the vast majority of lead contamination cases, it's either through oral means (wash yer mits!) or inhalation in an indoor range. I personally know one firearms instructor who has to quit his job at an popular local indoor range for this very reason. Lead styphnate is a main ingredient in modern primers and it's residue is hard too avoid indoors.
So in casting, use good basic hygiene and safety techniques and you'll be fine. Lead vapor is not on the reality list.
So, with lead in liquid phase hitting a vaporization temp at about 750 deg, isn't it giving off some small amount of lead vapor at this stage? What exactly is happening between that vaporization temp and lead's boiling point if it isn't lead vapors being released in some amount?