Philosopher's Stone

The Philosopher's Stone (賢者の石, Kenja no Ishi), also known by various other names such as the Red Stone, the Fifth Element, also the Sanguine Star according to Rz Rashid as shown in The Sacred Star of Milos, and the Grand Elixir in its liquid form and many more, is a powerful transmutation amplifier appearing in both the anime and manga. Due to the absolute law of alchemy being equivalent exchange, the stone gives the illusion that someone is able to override that law. Being that it is an illusion, the powers of the stone itself are not unlimited, and only appears to allow an alchemist to bypass equivalent exchange as long as the stone retains its power. Many of the main events in the series revolve around the Elric brothers' attempts to obtain this stone, in order to regain their original bodies, of whom had to be paid to the Truth in accordance to the laws of alchemy. It is also noted that the Philosopher's Stone only amplifies the abilities of an alchemist according to their skills and ability. This being the case, it may not always work while bringing a human back to life. If a solid body isn't present, it will not work and sacrifices will be made to substitute.

Composition
It is never explained in the series the exact process of creating a Philosopher's Stone, but it is known that human souls of those who have passed can be trapped and condensed with certain transmutation circles. These thousands or perhaps millions of souls make up both the power and physical existence of a Philosopher's Stone. It is a frequent misconception that the properties of the stone itself allow someone to override the law of equivalent exchange, but this perception is simply an illusion. The power of the Philosopher's Stone allows one to perform feats greater than what one can do naturally, but the stone gets weaker every time it's used because that power comes from the souls, which get consumed in these transmutations. When all the energy is exhausted, the stone also ceases to exist. The raw material of the Philosopher's Stone is a very large number of human lives, ranging from only one human life, to a few dozens, to a few million, or perhaps even more.

Appearance
The Philosopher's Stone can take many forms, ranging from a lumpy, coal-like rock to a viscous liquid, as with the one that Dr. Marcoh owns or even as a man (ex.: Van Hohenheim). Their color in the purely material form is always a dark, blood-like red. Usually the smaller it is, the less powerful the Philosopher's Stone.

History
The first stone in history was transmuted by the original homunculus later known as "Father", using the souls of the people of Xerxes. This event inspired the legend of a country which was destroyed in a single night. The later Philosopher Stones were transmuted by Doctor Tim Marcoh and his fellow alchemists who were instructed to make the Stones by Lust and the other Homunculi, using the lives of Ishvalan prisoners, and later the makers themselves to cover it up. This series of Philosopher Stones wasn't complete - they were made from only about 13 prisoners (based on the count shown in chapter 59). In the manga, the stone that Father Cornello used was also one from this series.

Generally believed to exist only in legend, the Philosopher's Stone has long been sought by alchemists as the ultimate goal of their craft. While alchemy is an amazing preternatural art in and of itself, its scientific limitations are such that the dream of a mystical and mythical object capable of eradicating those limits is one shared by generations of practitioners. Though in more pragmatic times, the legend of the Philosopher's Stone has come to exist only in the fanciful illusions of Romantics, the fabled amplifier is, in fact, an arcane reality.

In the 2003 Anime series, the first known stone was created by Hohenheim of Light and Dante around 400 years prior to the series. Both alchemists used the power of the stone to transfer their souls from their original bodies to others throughout the course of four centuries in an effort to live eternally. The stone later erodes away after Dante drains the last of its power to transfer her soul into Lyra's body, causing a Rebound that accelerates the decaying of the vessel, and thus, she desperately seeks the stone embedded in Alphonse Elric's armor body to continue living. There are also 'imitation' stones in this series, known as Red Stones.

Alphonse states that the name "Philosopher's Stone" is a reference to the object's status as "the thinking man's dream—reason conquering all." Later Basque Grand reveals the Philosopher's Stone has other names: The Sage's Stone, the Celestial Stone, the Great Elixir, the Red Tincture, and the Next Element.

In the manga/Brotherhood tie-in movie Fullmetal Alchemist: The Sacred Star of Milos, both Creta and Amestris have had soldiers fighting for control of Table City and the rest of the land of Milos for centuries over rumors that a Philosopher's Stone was in the city. At the same time, one of the legends of power that the Milosian people seek to harness to reclaim their independence is an object called the Sanguine Star. Ultimately, both these objects turn out to be referencing the same thing, as the Sanguine Star is actually a variant of the Philosopher's Stone which seemingly relies on many lives' worth of blood rather than actual souls for its creation making a humane but slow way of creating the Star possible. In fact, when Julia Crichton prepares to swallow a newly created Star, Ed warns her that it will consume her soul, which indicates a similar basis within the Star itself for deriving power from souls. He also states that the Sanguine Star which Ashleigh Crichton swallowed (to save his life) is warping Ashleigh's soul. It is only after both Crichtons regurgitate the Stars they swallowed that the brother and sister return to their own sense of self.

Red Stone
Though merely one of the various monikers attributed to the Philosopher's Stone in the manga storyline, in the 2003 anime storyline, a Red Stone is a separate, artificially synthesized alchemical amplifier modeled after the legendary Philosopher's Stone. Much like the Philosopher's Stone, the Red Stone allows alchemists to transmute without the aid of a Transmutation Circle, bypass the law of Equivalent Exchange in transmutation and even has the power to grant advanced alchemical skills to non-practitioners of alchemy. However, as an imperfect compound created by mundane methods, Red Stones lack the power of the true Philosopher's Stone and become unstable after a seemingly random number of uses, causing them to break apart mid-transmutation and run the risk of triggering an alchemical Rebound. Easily mass-produced, the Red Stones act as the primary mode of nutrition for Homunculi and are handed out to alchemists whose abilities and forbidden ambitions the Homunculi intend to exploit. In the 2003 anime, when within a special seal, Homunculi have been known to vomit Red Stones from their bodies such as what happened with Greed, Sloth and Lust.

Red Water
Unlike the methods by which the Philosopher's Stones are created, Red Stones are manufactured by compressing large amounts of Red Water into a single crystalline form. This crimson fluid is an extremely toxic-yet-powerful mixture of other alchemical amplification substances and can easily be produced in large quantities. Despite its high toxicity, it was discovered by the alchemist Nash Tringham that the most efficient and effective method of crystallizing Red Water is to introduce it into an existing biological process like the human body. Fortunately, his sons Fletcher and Russell later discovered that a similarly efficient crystallization occurs when Red Water is introduced to plant life.

It is likely, given the attributes of the Red Stone and Red Water, that they are modeled after Cinnabar.

Trivia

 * Morality is largely the only thing preventing the creation of a Philosopher's Stone.
 * Ed and Al gave up on finding one after learning its creation needed the lives of humans.
 * Dr. Marcoh fled the military after the trauma of creating so many got to be too much for him.
 * Central Command's top officers have no problem with sacrificing people (primarily death row prisoners) to create a few weaker stones.
 * Basque Grand was in charge of having Philosopher Stones made in Lab 5.
 * In the 2003 anime, a second barrier exists to forging a Philosopher's Stone: the strength of the Alchemist attempting to create it; Hohenheim nearly killed himself transmuting the Stone and was only saved by his lover Dante's intervention.
 * Despite the horrific method of creating a stone, if one already exists, most have no qualms with using it.
 * Alphonse hesitated to use a Stone against Pride and Kimblee until Heinkel assured him that the souls inside the stone were just as eager to defeat them as he was.
 * Edward hated himself to use Envi's Stone to save himself and Ling Yao from Gluttony's "stomach" until Envi assured him that now these souls have long lost themselves and will still never be able to return to bodies that have long died. It seems that Ed was able to come to terms with this later when he remembered that one of the souls thanked him for his release before disappearing.
 * Van Hohenheim seems to have started using the power of his Stone only when necessary, and then only after he was able to talk and make friends with each of the souls in his body and began to act with him harmoniously.
 * The Philosopher Stones break apart and vanish when they are used up; rarely, they will expel a massive rebound just before (as in Cornello's case). Though in the case of a human who is a living Philosopher Stone, they will rapidly age and show transmutation marks on their body.
 * It is interesting to note that in the manga/2009 anime, Van Hohenheim, being a human Philosopher's Stone, seemed to be able to use more power from his stone than anyone else, due to having individualized each and every one of the 536,329 souls within himself. The power seemed to be so great that Van was able to block several energy blasts from Father, which impressed him.
 * This could indicate that while the souls inside the stones are able to amplify alchemic abilities, when the souls are individualized, the energy that each soul willingly shares is of a much greater quality than if they were as a mass collection of souls with no true wills.
 * However, it seems because of Father's strength at the time, all the souls were burned up and left Hohenheim with only his own soul.
 * Both Ling and Kimblee show the ability to remain self-aware inside the Philosopher Stones of homunculi and even appear as their physical selves.
 * Kimblee enjoyed the sounds of anguish and despair in Pride's Philosopher's Stone, effectively a soothing lullaby.
 * Ling had a strong will, great mental discipline, and willingly shared his body with Greed. Compared to Pride's Philosopher's Stone, Greed's was quiet with no wailing from the other spirits.
 * In the 2003 anime, although Dante says at one point that she didn't know how to make a Philosopher's Stone, this could very well be a lie. It is more than likely that she was simply unwilling to try because of the risks involved when she saw Hohenheim craft the first one.
 * Because every human has a soul, each human is technically a Philosopher's Stone, allowing a highly gifted Alchemist to use their own soul to fuel transmutations. However, doing so is believed to shorten the Alchemist's lifespan.
 * Ed is the only known Alchemist to have achieved this. He used the technique twice.
 * Ed first used his own life force to heal himself after being injured fighting Kimblee.
 * The second time was in his battle with Pride; he transmuted himself into a Philosopher's Stone to confront Pride's consciousness with his own.
 * The concept of imitation Red Stones was derived from Edward Elric's conclusion that Father Cornello's Philosopher's Stone was a fake after seeing it run out of power and disintegrate. In the manga storyline, this is simply an incorrect assumption: Cornello's Stone had simply used up all its souls, and as Ed had yet to learn of the Stone's true origin, he initially believed the legend and assumed their energy was supposed to be infinite.
 * It is rumored that the Philosopher's Stone can allow one to complete a human transmutation. However, later rumors that it is possible to fully resurrect someone were dispelled:
 * Firstly, if the body has died, it cannot be restored, and the soul will not be able to attach to another body and as a result, sooner or later it will be rejected.
 * In addition, it is possible to perform manipulations only with the soul that is in any of the Stones or in the Gates of the Truth, but even with a stone it is impossible to return a soul that is neither there nor there and left this world going to the afterlife.
 * There is a plot hole related to the elimination of the consequences of meeting with the Truth: Van was unable to completely heal Izumi and return her organs, but later Marcoh was able to restore Mustang's vision with the help of a Stone.
 * Although, perhaps, Hohenheim could, but he just didn't want to return to Izumi what she had lost, believing that no matter what, everyone should pay for their actions.