Gems are the magical currency of Dominions, representing distilled magic power of a magical path. They are consumed by forging items, casting rituals, empowering mages to increase their magical paths, and casting certain combat spells. They are obtained mostly through magic sites, making site searching a critical activity for building up a gem economy. Other ways to obtain them include certain artifacts, some global enchantments, and to a lesser extent certain random events. Blood magic uses blood slaves instead of gems which have a number of mechanical differences discussed below.

As with magic items, gems can be freely allocated to any commander in a province with a lab, and may be returned to the stockpile in much the same way. In provinces without a lab, they can be passed freely between commanders. Because gems held by a commander that dies cannot be recovered, having another stealthy commander hold reserve gems to replenish those used in combat magic can be helpful in mitigating damage from mage deaths.

Gems may be converted from one type to another at rather great expense through alchemy. A very limited number of commanders may perform a much more efficient transformation with the carcass collector and pearl cultivator abilities.

Similarly to gold and magic items, gems may be traded between players. It is hard to assign a gold value to gems, as only earth and fire may be directly converted into gold through spells such as Distill Gold and Alchemical Transmutation. The gold return from such spells is based both on the magic path of the caster, as well as the alchemist ability.

Blood slaves are in many ways the gems for blood magic, but they have a number of key differences:

• They are primarily obtained through blood hunting. While magic sites can yield slaves, these sites are considerably rarer than those producing gems.
• Unlike gems, they are present in battles as another unit clustered around the commander which carries them. This does not affect their ability to be put on stealthy commanders, nor do they affect the map move of the commander carrying them.
  • This means that they can be killed in battle before they can be used for spells.
• Slaves cannot be used underwater. Blood slaves assigned to a commander which is underwater will immediately drown.
• Slaves on the battlefield can be used by other nearby blood mages (within a range of 8 tiles) that do not have any slaves assigned to them. If it is desired to use conservative gem usage with blood mages, all mages will need to have the option enabled, not just those with slaves assigned to them. Mages cannot use slaves assigned to hostile commanders, no matter the distance.

Mages can use gems in battle for three purposes:

• Some spells require gems to cast at all
• A mage can consume a number of gems up to their path level to reduce the fatigue required to cast a spell. For instance, a Fire 4 mage could consume four fire gems to count as a Fire 8 for the purpose of calculating fatigue for a spell.
• The *first* one of these gems also boosts the mage's path level for all other purposes as well.

For instance, the spell Relief requires a N5 mage to cast and requires 1 nature gem. A N4 mage could cast Relief with two gems – one to boost to N5 and the second to pay for the spell. They could spend up to two additional gems to further reduce the fatigue required.

Mages will only use gems in combat if they judge that the battle is significantly difficult; a single scout, or a handful of troops, will not provoke gem use from a large army.

As mages gain more research, they gain access to more and more powerful spells in combat that require gems to cast. These can be absolutely essential force multipliers – spells like Earthquake, Mass Flight, Fog Warriors, Antimagic, Mass Regeneration, and so on. Thus it becomes absolutely essential that armies stay supplied with gems to cast these spells. A large army can chew through many dozens of gems in a battle casting army-wide buffs.

It is often not a good idea to load mages with large numbers of extra gems; you risk losing them if the mage uses them for offscript casting, if the mage is killed, or if you lose the battle. Instead, you can use "gem mules", stealthy commanders (such as scouts) who follow an army carrying gem reloads.

There are a number of times when it is worthwhile to provoke a battle strictly for the purpose of causing enemy mages to expend gems. This is called "gem burning" or "gem baiting". It is most commonly done by provoking an earlier battle that the AI will take seriously enough to spend gems on; this is most often done by magic phase movement into a large army. In a variant, if a large battle will happen in a fort storm, the defender can break siege or move other forces against the sieging force to provoke it to spend gems, which will not be available in the storm battle.

Assassination battles can also prompt mages to use gems, including spells like Disease Demon or Earth Attack, or effects like Vengeful Water.