Q = Can these be heated directly in a bunsen flame and what temperature can they be heated up to?
A = Porcelain evaporating basins can be heated directly or when placed on a gauze, using a bunsen burner. Obviously the basins should always have liquid in them when heating, to reduce the risk of damage. If the intensity of heating is high, the flame should be moved around underneath the basin, to spread the heat more evenly and to avoid the build-up of hot spots. Unglazed evaporating basins can be heated up to around 1350 degrees C, whereas glazed basins can only be heated up to 1000 - 1100 degrees C. Grade A are more robust and can withstand stronger heating than grade B and should also withstand more cycles of heating & cooling before becoming damaged (they tend to eventually crack or crumble). Borosilicate evaporating basins can also be heated in the same way, but not to quite the same temperatures as if the glass is heated too intensely in the same place it can start to soften and deform. As above, just keep the Bunsen flame moving from time to time and they will be fine.