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A 2007 image from the Hubble telescope looking at the Carina Nebula in deep space. The image is often used to show the colors of the Phlogiston.

The Phlogiston, also known as the Flow, is a turbulent, unstable, multicolored, fluorescent gas (or gas-like medium) that fills the regions between the crystal spheres in the Spelljammer campaign setting.[1][2]

"The Phlogiston, The Rainbow Ocean, The Flow - an endless sea of every color" - gnome astronomer Hub-El, describing the unimaginably huge expanse between crystal shells


Also known as the rainbow ether[3] or the rainbow ocean,[4] the phlogiston is an infinite fog of swirling colors within which the crystal spheres bob up and down like enormous glass buoys. The term "phlogiston" applies to both the multicolored substance, as well as the entire region surrounding the crystal spheres.

The phlogiston has varying viscosity and forms dense rainbow rivers[5] or currents that lead from sphere to sphere, forming a vast three-dimensional web or network of rivers. Ships or creatures that move along these rivers of concentrated phlogiston find that the greater the density, the faster the current, which greatly facilitates interstellar travel time between spheres. A spelljamming vessel can control its relative speed somewhat by moving in and out of these currents. Further, the speed of the ship is partially dependent on the surface area it presents to the Flow, so many ships carry sails to capitalize on these vast currents to increase their interstellar speed.

The actual speed attained by a spelljamming ship entering a rainbow river is difficult to determine, since the phlogiston itself has no permanent landmarks. Time is the only constant. In general, it takes 10-100 days for a ship to travel from one crystal sphere to another. Spelljamming ships in the Flow still slow down when encountering other bodies, such as other vessels or rogue planets.

It is remarkably difficult to navigate a route to a specific crystal sphere, unless the ship's captain or navigator are experienced in travelling in the Flow, have charts detailing the appropriate rainbow rivers, or have access to magic or a locator device (supplied by the Arcane). Many rivers flow in both directions between crystal spheres. However, in certain cases a river will only flow in one direction, forcing a ship to travel via a second (or third or fourth) sphere before reaching its destination.

The crystal spheres float in the phlogiston like enormous corks on the surface of an ocean, and over time the spheres shift in position, drifting in and out of proximity to one another. However, the rainbow rivers almost never change course, meaning that navigating the phlogiston is still possible, its just that the sphere may no longer be located in exactly the same place. Fortunately, as the crystal spheres drift closer to one another, the phlogiston between them thickens to the point where it forces them apart, preventing collisions.[2][6]


  • Phlogiston is extremely flammable, like oil-soaked cotton wool, and is incredibly dangerous. Any open flame exposed to the phlogiston will cause the immediate area (including a ship's phlogiston-laden air envelope) to burst into flame. The resulting fireball rapidly expands to three times its normal diameter. For this reason lamps, lanterns or any similar device, as well as any weapon, such as a bombard or arquebus, which relies on a spark or flame to operate are strongly discouraged from being used in the Flow. Any fire-related spell, such as a fireball, immediately explodes in a ball of fire centered on the caster.
  • Because of phlogiston's flammable nature, crews extinguish all flame-based lights before entering the Flow. Phlogiston is luminous, meaning that light sources are not necessary on a ship's open decks. However, below decks and in certain dark regions, spacefarers rely on cold, natural lights (such as fireflies or fluorescent moss) or magical items to provide illumination.
  • Phlogiston cannot exist within a crystal sphere. It cannot be reproduced nor can it be collected and brought within the bounds of a crystal shell. If an attempt is made, whether physically or using magic, the ether simply dissipates, leaving no trace. Phlogiston simply cannot exist within wildspace or on the surface of a planet.
  • Gravity functions as per normal in the phlogiston, meaning that "down" is directed towards the major axis of a ship.
  • The ambient temperature within the Flow is similar to that of a cool summers day. However, there are no season within the phlogiston.[7]
  • Extra-dimensional magic or spells do not function in the phlogiston. This means that spells or devices that access other dimensions or planes, including bags of holding, portable holes, armor of etherealness etc. will not function in the Flow.[8] This also means that extraplanar creatures cannot be summoned into the phlogiston,[9] though they may physically travel into the Flow in the normal way. However, most sentient extra-dimensional beings prefer not to travel into the Flow, since they lose all contact with their native planes (with the exception of most undead who have a presence on the Material plane), and cannot gate in any support or use any of their dimensional-spanning abilities.[10]
  • The phlogiston has a preserving effect on living creatures that end up floating within it. In the void of wildspace a living creature would quickly exhaust what air they had left and suffocate. However, spacefarers that fall (or are thrown) into the phlogiston end up in a form of suspended animation. The unfortunate traveller falls into a deep torpor as their skin hardens and becomes grey as stone as their bodies calcify. Such castaways may float in the phlogiston for weeks, months or even years before being rescued. As soon as the castaway is brought into an atmospheric envelope they begin to slowly recover.[11] Those unfortunates who spent centuries floating in the Flow may be irrevocably altered in mind and body, becoming a creature known as a survivor,[12] while others may be collected by the monstrous creatures know as flowfiends and forced to become one of them.[13]
  • Most regions within the phlogiston look exactly alike, but there are a few known, and dreaded, inky black regions known as Dark Regions[14] from which few have returned. Unique to the rainbow ocean are the mysterious objects known as flow beacons. No one has ever determined who built these devices, nor what their purpose is.[15]

Planar Layout[]

The Manual of the Planes would have probably termed the phlogiston as a Transitive Plane had it been included in that volume, and in many ways, that's exactly what the Rainbow Ocean is. (It is still considered a part of the Material Plane, however, as are all known crystal shells). Nevertheless, there are features within the rainbow fog and even occasional phlogiston inhabitants.


External Links[]


  1. Dale "Slade" Henson, War Captain's Companion, War Captain's Guide, 1992, (TSR Inc.), Introduction, Concepts of Arcane Space section, pages 4-5
  2. 2.0 2.1 Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), The Phlogiston section, chapter 1: Arcane Space, pages 10-11
  3. Grant Boucher, SJA4 Under The Dark Fist, 1991, (TSR Inc.), The Phlogiston and Beyond section, chapter 2: The Golden Warrior, page 30
  4. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), The Phlogiston section, chapter 1: Arcane Space, page 10
  5. Grant Boucher, SJA4 Under The Dark Fist, 1991, (TSR Inc.), pages 2 and 16
  6. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), Movement in the Flow section, chapter 4: Movement & Combat, page 54
  7. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), Temperature section, chapter 1: Arcane Space, page 15
  8. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), Magic in Space section, chapter 2: AD&D Rules in Space, page 18
  9. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), Magic in Space section, chapter 2: AD&D Rules in Space, page 17
  10. Jeff Grubb, AD&D Adventures in Space, Lorebook of the Void, 1989, (TSR Inc.), Extraplanar Beings section, chapter 3 Spacefarers, page 60
  11. Jeff Grubb, AD&D Adventures in Space, Concordance of Arcane Space, 1989, (TSR Inc.), Castaways in the Flow sidebar, pages 28, 30 and 32
  12. Steve Winter, MC7 Monstrous Compendium Spelljammer Appendix, 1990, (TSR Inc.), Survivor entry
  13. John Terra, MC9 Monstrous Compendium Spelljammer Appendix II, 1991, (TSR Inc.), Flowfiend entry
  14. Grant Boucher, SJA4 Under The Dark Fist, 1991, (TSR Inc.), event 9: Give Us This Day..., chapter 2: Strange Bedfellows, page 16
  15. Ed Greenwood, SJR1 Lost Ships, 1990, (TSR Inc.), Flow Beacons section, Flotsam of Space chapter, pages 35-36