Flows of essence
The Flows of Essence were the feature of Shadow World "physics" responsible for allowing magic to exist. These "rivers of power" were invisible currents in the background essence, the aura projected by all things and especially living beings. The Essaence was a special kind of energy originating in a higher universe which was able to temporarily alter the physical properties of our plane of existence. While it was the foundation of all existence, so-called "planes" of existence ran along an axis of Order and Chaos. These more purely magical realities were able to bleed their properties into our world, which was on the threshold of an interdimensional rift.
The intersection of other planes with our own, or "pollution" with alien energies, is still described as a source of power in GemStone IV and DragonRealms. While the flows of essence were not unique to Shadow World, they were stronger there than any other known location. These bands of radiation were physical flows somewhat analogous to jet streams, moving through the air and below ground, as well as between the planet and its moons. It was possible for powerful essence users to ride the flows, such as the Lords of Liabo and the great dragons, or possibly airships in the hands of a skilled pilot. Flow riding used to be a spell that was never implemented.
Essaence
The Essaence was the raw power of the Flows, which when tapped was called Arcane power. In the I.C.E. Age world system, Arcane was an amalgam of the three realms of power, much as "hybrid" spell-casters combine two realms. While Arcane was the primal form of power that was the original form of magic, the Essaence is in some sense naturally decomposed into three realms. These were originally classified as "Essence, Channeling, and Mentalism" in terms of causal mechanism, but were later changed to "Elemental, Spiritual, and Mentalism" which reflect their typical spheres of effect. Very few were able to wield Arcane power, mostly Lords of Essaence or dragons.
While the gods would undoubtedly be able to cast Arcane magic, deities were actually self-aware Essaence nodes with limited personalities. They were able to will effects into reality directly, similar to what we now call Flow magic, and were virtually immune to magic themselves. Ultimately it would not matter, for example, if a Lord of Essaence was higher level than the avatar of a deity. It would be very difficult to kill a god without the aid of another god.
Essence
The essence is best thought of as the background radiation that surrounds and permeates all things. Essence wielders would directly change patterns in the Essence to "dictate the flow of events, and the course of life itself." These temporary pattern alterations allow them "to redefine the reality around them, molding elements and wielding very real power." The imbalance would work itself out, but the effect of the spell would remain. The essence was especially prone to balancing itself with elemental effects, with Wizards being specialists in elemental evocation magic. Since the "extension of one's life essence" is used to alter patterns outside the body's "immediate sphere", unliving material and especially metals could inhibit attempts to manipulate patterns and thus prevent magical effects. However, the Essence realm was not tapping "the raw Essaence" of the Flows, which was the realm of Arcane power.
Channeling
Channeled power would come directly from a source such as a deity, being "channeled" through the caster who acts only as a conduit. These would be projections of effects using the sphere of emanation of a deity, the aura projected by some immensely powerful being rather than tapping the essence itself. In other words, it is the source of the power that is manipulating the patterns of essence, with the mediator having some magnitude as a conduit. Consequently, channeling was not spell-casting as such, but rather invoking spell-like effects through themselves. These spells were often spiritual in nature, later becoming the Spiritual sphere.
Mentalism
When the spell-caster manipulates only their own aura, rather than "extending" themselves to manipulate their environment, they are in some sense channeling their own essence. In other words, mentalists were miniature imitations of the gods, manipulating their own essence as though it were their sphere of emanation. However, their limited scale as corporeal beings meant that their powers were largely limited to manipulating their own bodies or immediate surroundings, often in the form of mental effects and so called "Mentalism." Sorcery was often notable for its mental effects, in spite of not being "mentalist", because it was manipulating the essence of the target.
Physical Behavior
The Essence was prone to currents called the Flows of Essence. These flows would have numerous unusual effects when interacting with the physical environment. Since the essence originated in another universe, it would interact in predictable but exotic ways with the forces of our own existence, which itself was founded on a more banal kind of essence. These were mostly stable configurations that would not have magical effects, but occasionally there would be imbalances or backlashes with exotic consequences. Celestial alignments were especially likely to cause problems by pulling upon and crossing flows between those bodies and the planet.
Flows
The flows of essence were rivers in a special kind of radiation field. Strictly speaking, a "flow" of essence would be any fluctuation in the essence field, whether in space or time of any scale. However, there were large scale currents, largely in a steady state. They would twist in three dimensions, found both high in the air, as well as deep underground. These existed across a range of powers, with stronger flows being formidable forces on the environment, blocking weather patterns as if they were a mountain range. Jet streams often followed along Essence Flows. The Navigator home isle had a powerful artifact that tracked the flows across the world by representing them on an enormous sphere.
Greater and lesser flows were fairly stable over long periods of time. They would converge on essence nodes of corresponding scales of power. Their convoluted path was partly the result of interacting in some complicated way with the magnetosphere, which made compasses useless for most people in the Shadow World history. It was not known which was the more dominant force, as they mutually drove each other allowing exposure to various kinds of radiation. The magnetic field was always in flux, making pole flips much more frequent. The extent to which this is still true for Elanthia is not clear.
Koar was known to be able to control the lesser the flows, with some limited influence upon the greater flows, which has a lot to do with why he was originally supposed to be able to control the weather. The flows were partially replaced with the term "mana pools," which became a distinct concept related to infusing background energy for enchantment. Wizards are able to SENSE both earthnodes and mana pools.
Nodes
The Essence had a tendency to form foci, called "earthnodes", that were either temporary or permanent. These were convergence points for the flows of essence, so magic that involved transport guided somehow by the flows would tend to drop out at them. These existed on multiple scales of power, depending on how strong the flows were that fed into them. More powerful flows tended to be stable, and so more powerful nodes were less likely to be temporary or transient. In contrast, there would be short-lived minor nodes formed by fluctuating minor flows, even artificial ones by pulling upon them in a local area.
- Major Nodes
There were half a dozen "Key Foci" in Shadow World. The most famous was the site of the Navigator home isle, which consisted of three curling "arms" of power whirling out from it. These warded off lesser flows, as well as Flow storms. However, if a flow storm were to anchor on a major foci, it would probably end up engulfing the whole planet. These would not last forever, but it would nevertheless be rare and devastating.
- Greater Nodes
Supposedly "hundreds" of greater nodes exist. These were often rooted to a specific location or tied to a large object (e.g. great crystal sphere), and many had been marked with monuments or buildings intended to exploit their power. Greater foci were more likely to exhibit disturbances that gave away their status as concentrations of essence. These symptoms included several common varieties: (1) Faint shimmering, akin to heat distortion. (2) Tingling sensation, like static electricity. (3) Scent of ozone. (4) High pitched whine, or almost sub-audible thrumming. (5) Feeling a shiver.
These effects still exist for special locations, especially in the older parts of the Wehnimer's Landing region. (However, some of these are no longer actually nodes, they just have the symptoms of it.) They often happen as disturbances in flow storms, or when the fabric of reality is badly warped. Whenever a god has a concentration of their own power as a "holy site", especially the focus of their sphere of emanation, these effects are especially likely to happen. Meyno's Shrine was a greater focus, for example, before she was released from it. This is unrelated to the concept of "supernodes" which maximize experience absorption.
- Lesser Nodes
Lesser foci tend to be virtually invisible, unless a skilled essence user were to detect their presence. Most magic users will not know they are on a node unless they happen to notice they are drawing more power when the flows pulse than they would usually. Experience absorption in GemStone is more rapid when upon a node.
Barriers
Essence barriers are walls of two kinds that prevent things from moving through them. These are usually invisible. "Physical" barriers manifest themselves as some "unseen force" preventing motion, which exist both naturally and artificially as wardings. Familiar examples include the archway inside Hearthstone Manor and the Path of Enlightenment in the Voln monastery. Wall of Force (140) is a barrier surrounding the target. In principle, any such barrier can be overpowered, with sufficient force. More subtle are "mental" barriers, which misdirect those who encounter them. The forest leading up to The Graveyard is the most familiar example.
Flow Storms
When the flows of essence become wild, typically as a backlash of some excessive power, they will typically manifest in weather disturbances. Minor backlashes might take the form of clouds shooting out a beam of energy, whereas a severe disruption will result in a Flow storm. These hurricanes of magical power usually discharge elemental effects, though often are unique or strange, with severe winds and seismic disturbances under certain conditions. They might tear open random voids into nothingness, or form portals to other planes of existence.
Flow storms can be extremely dangerous to anyone attuned to the Essence. They tend to dissipate over weeks or months, though they can become permanent if they anchor on a source of power. Storms might be triggered by celestial alignments or too much power being drawn from the flows in a given area. Portals are often too dangerous to close due to their backlash risks.
Behind The Scenes
Flow Patterns
Planar Shift (740) works by sensing the "flow pattern" in a given location to record it runes. These "threads" of magic are followed when stepping through a rift, with the sorcerer guided along to the target location. In theory this is consistent with the "physics" of the flows of essence. Greater and lesser flows are stable and would uniquely configure sub-regions of the continent. While minor flows were supposed to be transient, they may be stable enough to give specificity. The spell is able to give cross-realms transport, circumventing the natural essence barriers, which are typically strong flows of essence within mountain ranges and so on.
Elemental Detection
Elemental Detection (405) detects whether objects are suitable for imbedding by whether or not the flows of essence are drawn to it. When the items are unsuitable, the essence forms a chaotic pattern around it, reflecting the transient eddies in the background radiation. It is not possible to make any sense of the patterns.
Elemental Wave
Elemental Wave (410) was based on the idea of "pulsing" the Essence in the surrounding area, forming a transient essence barrier that knocked everything down. The more powerful version that came later, Major Elemental Wave (435), discharges elemental effects as critical damages.
Mana Focus
Mana Focus (418) attempts to "gather" the (minor) flows of essence in the area to form an artificial node. The less powerful the caster is in terms of level, the more likely they are to be subjected to a backlash. When this is attempted in an actual node it is tantamount to playing with more powerful flows, which will end badly for the caster who attempts it. Most spell-casters cannot expect to be as talented at manipulating the flows as Koar.