Ink

Sometimes known as Murmur's Ink, generally referred to as such in documents to avoid confusion with actual ink.
Branch of sorcery developed by a pair of Kraken-based Murmur to make use of their enhanced regeneration when in proximity to water. Functions by soaking water with gaseous "solid" shadow in order to Celestially claim and manipulate it. This process is naturally uneven due to the turbulent nature of the fast moving water, resulting in the darkness swirling similarly to ink, earning the practice its name.
Use of Ink allows for the existing medium (water) to take the brunt of impacts instead of transferring it directly to the user's energy construct, improving efficiency. In an area with large bodies of water, it allows for a massive amount of battlefield control (at high energy cost for soaking all that water in shadow). Enemy clothing soaked in Ink can easily be made far more rigid, drastically hindering enemies' abilities to defend themselves.
Outside of its creators, pure ink usage is rare due to both the energy cost and difficulty in finding information on the subject. Smaller techniques and tricks have proliferated throughout sorcerers over time, generally originating from those in Krakenmount. For example, the act of pulling water along with one's shadow whip improves the coherency of the spell and its overall energy efficiency (at the cost of being trickier to maintain and dissipating after one good hit). Gaseous shadow used to expand one's area of influence is incredibly popular, the technique also originating Ink, being the first 'branch' of sorcery to successfully project a gaseous substance coherent enough to exist for extended periods of time.
Ink is similar in concept and execution to xiphaem and the original earth-manipulating techniques which eventually developed into northern arcanism.

Xiphaem comparisons

Ink is an interesting counterpoint to Xiphaem because it was created by Murmur, somebody without blood. As a result, they don't get the standard efficiency boost and ease of claiming that ordinary humans will with blood, and built their own sorcery medium to achieve similar results while working around this fact. On the other hand, the same ritual which took all their blood also granted them a Conceptual Alignment towards water.
People other than Murmur don't get a significant efficiency boost out of using Ink rather than projections like Hard Light or Solid Shadow. It remains useful for its particular properties that differ from said materials (e.g. surface tension, mass), but isn't an overwhelmingly powerful choice in the way it is for those with a conceptual alignment.