In The Way of Kings when Jasnah uses her Soulcaster to defend herself and Shallan against the 4 thugs in the alleyway, the book describes how one of the gems on her Soulcaster cracked from the strain of using it to much. Later on, Shallan discovers that

the Fabrial is indeed a fake and Jasnah can Soulcast without it.

According to that, why did the gem crack when Jasnah Soulcasted - she didn't use the fabrial and she couldn't have broken it intentionally with Soulcasting because gems can't be Soulcasted?

  • 1
    She was still using those gems, just in a different way.
    – Mithoron
    Jan 10, 2019 at 16:14

2 Answers 2


Soulcasting is a fairly unique form of Surgebinding, and seems to behave in a similar way to how a soulcasting fabrial works. Soulcasting surgebinders seem to be able to take the stormlight directly from gems for soulcasting without taking the stormlight into themselves. When this happens, the surgebinding behaves like the fabrial does; you take stormlight from specific colour gems based on what you are soulcasting into. See this "Word of Brandon" (emphasis mine):

STORMATLAS: I finally got to ask a question about the Stormlight Archive that Windrunner17 and Chaos helped me with which was: "Why Can Kaladin Surgebind with any gem type but Jasnah and Shallan need specific types?"

BRANDON SANDERSON: A lot of that will be explained as the series comes along. It is really the difference between Soulcasting and the other forms of Surgebinding. It's more a quirk of Soulcasting than it is something that is different about about Kaladin. So you've kind of got it reversed a little bit though; Soulcasting has this additional restriction that the other ones don't.

source (question 4)

It seems as though soulcasting is unique in surgebinding in that the stormlight can be directly fed into the object being soulcast from the gem, without being sucked in; and the gem colour affects what changes can be made.

As far as the cracking gem aspect goes, that part could be explained even if she were drawing stormlight into herself for the soulcasting. Gems shattering appears to be a consequence of taking too much stormlight out of a gem too quickly (along with the fact that the gems in circulation have imperfections). It's similar to cooling down something too quickly, you create a stress in the gem and it cracks. Or at least that seems to be the common accepted theory. Some discussion on gem cracking can be found here.

Now, in terms of pure speculation, it seems as though gems are acting as some sort of "key" in the soulcasting process. This reminds me a lot of other similar circumstances in the Cosmere. Metals on Scadrial are keyed to allow access to Preservation's power, and the type of metal changes how the investiture manifests. Aons in Elantris are keyed to access the Dor, and the Aon used changes how the investiture manifests. It stands to reason that by the same Cosmere logic, the gemstones may be acting as keys which allow the stormlight to change the objects, and they keying affects which changes are possible. Again though, that part is more speculation without any direct support.

Some additional discussion on Jasnah's soulcaster can be found here and here.

  • interestingly enough, the color of the gemstone makes more of a difference then the composition (see the ars arcanum in oathbringer) which bears some resembelance to the way investiture works in warbreaker
    – Antheloth
    Jan 24, 2019 at 14:07
  • @Antheloth I think it's a really interesting mixture of Warbreaker's more subjective system with Mistborn's more concrete structure. The colour of a gem is definitely a by-product of the composition, which aligns with Mistborn pretty well. At the same time, very small structural changes can quickly change the colour of the whole gem. So it's still a change in composition; but unlike metals, a very small change in composition can change the colour dramatically, so the way the structure interacts with the power seems more related to cognitive aspects than it is in Mistborn.
    – JMac
    Jan 24, 2019 at 15:09
  • if you read the ars arcanum it says explicitly that its the color
    – Antheloth
    Jan 24, 2019 at 16:58
  • @Antheloth The colour is just a function of it's composition though. It's more subtle than allomantic compositions, where "close enough" generally still works, because small changes to composition can dramatically change the colour. The colour of a gemstone is definitely due to it's composition though, that is what I am saying. It's in-between ground for Warbreaker and Mistborn. In Mistborn it's metal composition, but colour is not a reliable way to recognize that (barring spectral analysis). With gems, the colour is highly sensitive to composition, but it still comes from that.
    – JMac
    Jan 24, 2019 at 18:19

When something acts as the stormlight "tool" it is put under strain. For example, gems crack in all types of fabrials, (as far as I'm aware,) if the stormlight is forced to be used more than the container, or the tool can handle.

Repairing shardplate generally cracks the gems aswell, as it takes such a large amount of stormlight for it to repair itself.

Surgebinders bodies are also, after excessive stormlight usage, usually exhausted. This is because the bodies of the surgebinders are the tool under strain in this situation.

I assume that if you only soulcast small individual objects, the gems would be perfectly fine and never crack.

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