A Beginner’s Guide to Drucraft #14: Blood Limit

You can’t use someone else’s sigl. 

More than any of the other four, the Blood Limit shapes the drucraft economy.  It is the primary reason that sigls are so expensive.

Just like the gemstones they resemble, sigls can last a very long time.  They’re short-lived in geological terms – aurum naturally sublimates into free essentia, and if left for long enough, a sigl or a lump of aurum will wisp away into nothingness.  However, ‘long enough’ on a human timescale is a very long time indeed, and a solid sigl can easily last for thousands of years.

This raises an obvious question – why isn’t the world filled with sigls?  Nowadays the vast majority of sigls are threaded rather than solid, with exponentially shorter lifespans, but even if only five percent of the ones made each year were solid ones, that’s still an enormous number that would only continue to accumulate century after century.  So why are they in such short supply?

The simple answer is that a sigl made for one person won’t generally work for another.   There are indeed vast numbers of sigls in the world, sitting in museums and bank vaults and private collections – it’s just that the vast majority of them can’t be used, since they were made for wielders who are now long dead.  Thus, while the absolute lifespan of a sigl can be measured in thousands of years, its practical lifespan is, in generational terms, very short.

Anatomy of a Sigl

Sigls are comprised of three layers.  The outer layer, known as the shell, is an ablative and largely inert coating designed to protect the sigl from erosion and damage.  The middle layer is referred to as the body or outer core, and comprises the majority of the sigl’s mass.  However, it is the inner core, otherwise known as the kernel, that is the reason that the Blood Limit works the way it does, because a small but critical fraction of the kernel is made up of the wielder’s personal essentia.

Shaping a sigl with someone’s personal essentia is something like forging a lock with a human key.  It’s the only reason that sigls work at all.  Making a sigl without any personal essentia just produces an inert lump of aurum, and trying to use a sigl whose personal essentia doesn’t match yours is impossible.

This means that if you want a sigl, you can’t buy one second hand.  You have to either make one yourself, using your own personal essentia to shape the kernel, or have a professional shaper take a sample of your personal essentia to make one for you.  Most people pick the second option.

The result of this is that the drucraft economy doesn’t work like the markets for manufactured goods such as jewellery or furniture, where the products can (in theory) be maintained indefinitely.  Instead, it follows a cycle where new sigls are created, remain in circulation for a finite time, then disappear.


The Blood Limit is probably the most extensively studied of all of the Five Limits, and the workarounds to it are well-understood.

The simplest workaround is to have the shaper, when they create the sigl’s kernel, mix in someone else’s personal essentia with their own.  Creating such ‘mixed sigls’ is inherently more complex than creating a pure one, but the techniques for doing so have been exhaustively practised over the centuries and the procedure is now quite routine.  However, you don’t get something for nothing:  the more of someone else’s personal essentia there is in a kernel, the weaker the sigl will be when you try to use it yourself.  This method is thus less of a true workaround and more of a compromise.

The second (and more famous) method is to use a sigl belonging to someone whose personal essentia is sufficiently similar to yours.  This generally requires the sigl’s creator to be a blood relative, the closer the better.  In this way sigls can be passed down from parent to child, or from sibling to sibling.

This method is not infallible.  The closer a blood relation two people share, the more similar their personal essentia tends to be, but there’s still variation.  Parent to child or brother to sister almost always works, but it’s not a guarantee, and as the relationship becomes more distant, the chance of the sigl working drops like a rock – two ‘steps’ in the family tree is usually the realistic maximum.  And this assumes a pure sigl, rather than a mixed one.  If the sigl was shaped by someone else, the  personal essentia in the sigl is effectively diluted twice over, reducing the viability even further.

Still, even with its drawbacks, the ability to pass sigls down to the next generation is incredibly powerful.  Even if you can’t get more than two generations worth of use out of a sigl before it becomes useless, that still represents an enormous advantage over anyone who uses a sigl for only one.  The concept of inherited wealth takes on a whole new meaning when children can inherit not only a house and money from their parents, but magical powers as well.  This is a major reason for why the equivalents of Drucraft Houses developed independently in so many places around the world . . . and even in countries with no House traditions (or in ones where such practices are specifically banned) family-run corporations and political and financial dynasties fill the same role, passing down their wealth in exactly the same way.

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10 Responses to A Beginner’s Guide to Drucraft #14: Blood Limit

  1. Allan says:

    The point about sigils piling up over time raises another thought I had. Let us assume that a given solid sigil will last, on average, 500 years or so (just to pick a number mostly at random). Obviously, the blood limit will strongly limit how much practical use that sigil will see (unlikely to be more than 200 years, let’s say), but the essentia used to make it is still ‘bound up’ in there for that 500 years.

    Now, when sigils are made relatively uncommonly, that’s not a big deal. But it sounds like the sigil manufacturing is moving more towards industrial or semi-industrial systems. The blood limit still means sigils need to be more-or-less custom-made, but since there are obviously more or less efficient ways to do it, it’s *plausible* (although by no means certain) that there will be more innovation and improvement in that – we can theoretically conceive of a world in which solid sigils can be made let’s say an order of magnitude more cheaply or easily than current times.

    If we accept that hypothetical, does this create a potential ‘running out’ of essentia? Not true running out – the sigils will eventually sublimate back – but within the scope of human generation the difference is somewhat academic. And if that occurs, what would it look like? The way essentia and Wells are described it sounds like it’s not that they ‘generate’ essentia, but more Wells are just collection points, and living beings just interact with essentia rather than making it. Which implies a limited (if potentially truly massive) supply.

    I don’t know, I’m probably missing something. But it seemed at least not obviously implausible as a hypothetical scenario, even if it’s one that’s unlikely to come up within the scope of the actual series and story you’re telling.

    Very keen for Book 2 and 3!

    • Benedict says:

      You’re right that that’s how the process works – however, on a global scale, the fraction of essentia on Earth that’s locked up in sigls is like the fraction of water on Earth that’s locked up in ice. Even with industrialised sigl production, there’s currently no likelihood of essentia running out.

      Given hundreds/thousands of years and advances in sigl creation, however, it IS theoretically possible that a scenario that you’re describing could happen, in which case Wells would gradually become weaker, causing average sigl strengths to steadily drop and sigl prices to steadily rise until they reached a new equilibrium.

  2. Andrew says:

    Is there any market at all for those old sigls?

    What would a jeweller who didn’t know drucraft think they were made of?

    • Benedict says:

      A jeweller would just think they were another type of precious/semiprecious stone. Unless they’d had it explained to them that there was something special about this one in particular.

  3. Bill says:

    Thank you very much for such a comprehensive update on the Blood Limit. However I have a few questions:
    Does using the Sigl of a close relative have any effect on the Sigl power or is it just a works or doesn’t type thing?
    Is unravelling the essentia bound up in a sigl a simple process (and could Stephen, if he tried, probably work out how to do it? Also, what essentia loss is there in this process? For example if to initially make the Sigl it had drained a B Class Well would there be the equivalent of full D Class available for Stephan to use?
    Maria told Stephen that one could get around the Blood Limit by using a persons blood. I assume that this is to avoid those who can afford Sygls having to be present during the lengthy construction process. But how does this work, does blood continue to produce personal essentia when distant from the donors body and how long can it continue to produce it? I’m assuming stronger sigls need more essentia and more essentia means more blood?

    • Benedict says:

      One of the factor’s affecting a sigl’s power is its attunement level. A sigl made 100% with your personal essentia is fully attuned; anything less than that proportionally decreases the sigl’s effectiveness, and there’s a minimum floor (around 20%-30%) below which a sigl won’t work at all. Attunement’s a big subject and is going to be the subject of its own article.

      Unravelling a sigl into essentia is quite straightforward – it’s a Primal effect, and Stephen could absolutely learn how to do it. Capturing that essentia and turning it into a new sigl is much, much more difficult, and always comes with some degree of wastage.

      Any part of someone’s body retains their essentia ‘signature’ for a while, meaning that free essentia that flows through it takes on the qualities of their own personal essentia. Blood’s a popular choice because it’s the easiest part of a person’s body to extract in significant quantities without causing lasting injury. It’s actually easier to just use the person, but there are security/secrecy reasons for Houses and corporations to prefer not to have their customers present at their Wells.

      • Felix says:

        If the well holds the essence, then why doesn’t Steven “discharge” his failed sigls of invisibility in the Well of Light? Then the loss of essence would be minimized, and the immature well would be filled.

        • Benedict says:

          This is actually something that can be done, but (a) as of book 1, Stephen doesn’t know that it’s possible, and (b) it’s a relatively advanced technique that requires some skill to pull off effectively.

      • This was one of my big questions from the article. If the physical life of sigls is so long, and wells are so fought over, it surprises me that there isn’t a bigger market for the resale of unusable sigls for recycling into new sigls.

        Sure, maybe powerful rich families have their own wells and no need for recycling.

        All it takes is a few nouveau riche families and old families whose well somehow dried up to create a demand for recycling. Even if the families with wells had a policy of keeping their sigls as strategic reserves, I imagine there would be poor or profligate family members on the fringes willing to sell the sigls, if they could get their hands on them.

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