Keith, it is said that 'the pen is mightier than the sword'

Now I don't believe this is meant in anything other than a figurative sense although some written criticisms of Israeli government policy and breaches of international law here appear to have produced a predictable patellar reflex

So while the adage is obviously not meant to be literal, what is obvious is that if you deliberately stab your pen in the eye of an adversary then you ar using it as a weapon

Once more

White phosphorus is an indiscriminate killer that ignites once it is exposed to oxygen, producing such heat that it bursts into a yellow flame.

It has thermal properties which burn by heating everything around it, rather than chemical properties which attack the body's life systems . It therefore does not fall under the 1993 Chemical Weapons Convention.

But protocol III of the 1980 Convention on Conventional Weapons bans its use as an incendiary weapon against civilian populations

The treaty also restricts their use against military targets "inside a concentration of civilians except when such military objective is clearly separated from the concentration of civilians".

The use of White Phosphorus solely as an obscurant in battlefield conditions is legal. However.......

"Article 1 of Protocol III of the Convention on Certain Conventional Weapons defines an incendiary weapon as 'any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance delivered on the target'.
The same protocol also prohibits the use of incendiary weapons against civilians (already forbidden by the Geneva Conventions) or in civilian areas.

This protocol is only binding upon those who have signed it; the United States, has not signed or agreed to Protocol III. - Wiki

While the United States opted out of signing it descxribed the use of WP by Saddam Hussain as a chemical weapon although the Chemical Weapons Convention does not list WP in its schedules of chemical weapons

Saddam's use of WP against civilians in 1991 was included on the list of war crimes which was used in part justification of the 2003 invasion.

Incendiary weapons: The big white lie

'Mike Gapes, the Labour chairman of the Foreign Affairs Select Committee, said: "I think there is an issue here about whether the chemical weapons convention should be strengthened to include this particular substance because it is defined as an incendiary not a chemical weapon, therefore it is excluded from certain definitions." '

parlimentary report 2005