How to identify leaded balls or lead-free balls with eyes ?

How to identify leaded balls or lead-free balls with eyes ?  If you want to install a bga chip , you need to know it's balls is leaded or lead-free before you installing , Because their melting point is not same , leaded balls' melting point is 183 Celsius , lead-free balls' melting point is 217 Celsius .
So their installing temperature are different .  How to confirm it is leaded or lead-free balls with your eyes only ? 
1, from a bga chip ,  In appearance the surface of leaded balls is shiny white , uniform light .  If oxidation we can wipe clean with an eraser . The surface of lead-free balls is faint yellow . Colour and lustre are uneven .  
2, We wipe balls with hand , if left black mark on hand , then it is leaded balls , if left faint yellow mark on hand , then it is lead-free balls .Your loyal friend - Pinkney , http://www.htic-tool.com   

from https://plus.google.com/b/107329939332162905445/+Htictoolchipset/posts