I will see to it after I understand how you're trying to implement it. In the videos, I've simply downloaded a completely fresh copy of v19, with nothing changed except to raw/objects/inorganic_metal. The changes of which was simply to copy the code given in the OP onto the bottom of the document (But above the entry for adamantine, so in between adamantine and Bismuth Bronze). Nothing more nothing less, if it still doesn't work, I'll upload a copy of the entire thing.
Hmm i recreated it doing as you said however the most interesting thing is that i then tried again with my old copy and it worked perfectly with nothing changed. As the doomium exploded instantly there is no way i would have missed it before.
I can't explain it but at least it is working. I am extremely grateful.
I'll see if i can get the arrows to delay their explosion now and if it is successful then i'll move onto grenades.
EDIT:
1) There is no 'slow melt', it'll be gone as soon as it's created, unless you set it to melt upon achieving body temperature, in which case it must be 'embedded' into a creature to work (Well, in adventure mode maaayyybe, if it's a really sharp vial).
By increasing the spec heat i have increased the time it takes to ignite the material. even if putting it in pots is impossible being able to produce a grenade that will go off a certain time after it is created could be very useful.
I am having trouble making the material dangerous to bystanders though. most of the time the arrows dont even kill the guy holding them. It's early days though and still a lot to try.
EDIT2: Oh also and i have found the cause of the problem. It's something to do with taking control of a person in the arena. Seems to stop it working until the arena is reloaded.
EDIT3: Seems it is not possible to make a grenade as they will not melt/ignite when just left to the air.