17) The metal heads contain a high level of arsenic, it’s not known why
18) Some Ife traditions say members of the generation of casters that produced the Ife heads may have been executed by an Ooni in anger.
19) And some historians say members of the Ife head casters may have died from arsenic poisoning as a result of working with high levels of arsenic.
20) Of the 3 crowned heads, one is housed in the British Museum, and the other in Ife Museum. The third is “lost”.
Bonus Fact: Its very difficult to find royalty free images of all 19 Ife bronzes.
http://theyoruba.com/2016/03/01/ife-bronze-heads-20-things-you-should-know/
Very informative