Fireblood Elixir is a dark fluid, kept carefully dealed in vials with self-healing membranes for lids; taken via injection rather than imbibing in the fashion of most elixirs, habitual users often complain of an ashen taste to everything they eat, and the alchemical concoction is visible in the blood as a dark stain in all visible blood vessels, making them stand out vividly against most skin; eyes in particularly are transfigured, the white sclera turning a smoky grey color for the eight hours or so that the elixir is active in a user's system.
Exposed to open air, the lquid rapidly harden, forming a glossy crust within minutes of exposure; an entire pint of the liquid - enough for numerous doses of most average-sized humanoids - will harden into a glossy, obsidian-like lump within a day, with higher grades hardening more rapidly. This lump is exceptionally combustible, with even a slight spark from an aetheric discharge sufficient to ignite it and bring it to temperatures capable of burning through hardened steel.
Fireblood elixir takes roughly five minutes to circulate enough to be effective; after this time, the chemical has bonded to a large number of red cells in the blood. The bond acts to dramatically amplify the carrying capacity for oxygen of a given red cell, allowing users to extract more oxygen from each breath; in addition, the compounds selectively strips carbon from CO2 waste products, binding it to the compound and freeing the O2 to recirculate. While some is lost, this property allows users to go for startlingly lengths of time between breaths if desired, as well as easing cardiovascular stress during periods of exertion - such as combat.
This is merely an incidental side effect to what happens when a fireblood user is wounded in combat, however; any injury which draws blood causes an abrupt and violent oxidization as the augmented red cells tear oxygen from the air to which it is exposed, releasing a gout of white-hot fire from the injury for a bare moment before the flames cauterize the wound. This is amazingly painful to the user, with those who have experienced it insisting it is a far more intense pain than regular cauterization; it is also extremely worrying for enemies, as the gout of fire is intense enugh to incinerate cloth, ignite leather, and flash-heat metal to temperatures capable of burning flesh in contact with it.
One final benefit of the elixir is that very few poisons or other foreign materials - such as Troll flesh - are capable of surviving the intense fire, making it somehwat more popular among those who routinely fight foes who rely on such augmentations in combat.
Fireblood Elixir is typical of goblin thaumatechnology, with the elixir doing what the creator expected while having easily-anticipated and hazardous side effects. The creator was a goblin alchemist who knew of the practice of cauterization to save badly wounded soldiers from death; he reasoned that self-cauterizing wounds would free up time for the overworked medics to deal with other cases, and set about creating something to accomplish this. It took nearly a year and a half, with three laboratories burned down by uncontrollable fires and numerous deceased test subjects, before the finished elixir was finally produced.
It was wildly popular for roughly a month, with the city-state of Vahani outfitting every soldier with a supply for the next raid from the deformed barbarians of the Thaumic Wastes; during the first skirmish, more soldiers were incapacitated by pain from the cauterized wounds than the enemy, who broke ranks and fled when their chieftan was immolated upon beheading a dosed soldier. Now, it still sells, but only to elite military forces who regard a resistance to pain as a sign of true warrior spirit; very few orcs express any enthusiasm, despite their fondness for ritual scarring, as the heat of the flames often destroys their more delicate tattoos and scar-paintings, while the elves of the Vular wastes regard it as a marvel of high thaumatechnology, using their own burning blood as a weapon in combat more often than their more mundane armament.