What qualifies as a surface in Glyph of Warding?

Question

Can a player specify the surface of a small object as the surface affected by Glyph of Warding?

One of my players decided to create guns in the world (there are no guns present until now) by having bullets constructed and putting the glyph on the flat end with the trigger as "Be struck by metal". He was going to have it at the end of a metal barrel with the trigger causing a small hammer to strike the flat end (Glyph) of the bullet triggering it and the force propelling the bullet forward. (He has also convinced an exiled dwarf smith willing to work with the "bloody complicated contraption.")

I conceded that the explosion will be smaller, he still needs to take a saving throw to not drop the gun and that it will be difficult to construct, load and operate. However one of the players argued that it's not a surface but rather an object that is being glyphed, so moving the bullets with you would break the spell without triggering.

Answer 1

Normally I'd say that this kind of use is a stretch, but in this case I'd say it works, for one very critical reason: you, the DM, are on board with this.

In my own game I would rule against it: a glyph on a surface is measured in feet in the spell's description, and regardless of it being vague otherwise, I would feel quite within my responsibility as the arbiter of the game reality to say that something so complex that it's normally measured in feet could not in any way be reduced down to mere fractions of an inch. (At this point I would also point out to the player that if they're determined, they can just research a new spell that does what they want directly instead of trying to press an ill-suited spell into service.)

However, this is your game, not mine, and the same principle applies: you are responsible for arbiting the game reality. And in this case, you are clearly on board with the player's use of the spell. You even have supplied a cooperative NPC dwarf to get around the problems of engineering that took centuries to solve in our own history of firearms!

The only issue seems to be that you have one (or more?) other player who isn't so on board. In this case, since you are willing to grant the use of the spell, your problem is not the spell, it's mollifying the objecting player(s).

To do that, reassure them that the ruling is in the best interest of the game being fun, which is the ultimate goal of play. "The spell is vague on that point. It's obviously not casting it in an object, so the object rules don't seem to apply, just the surface ones. It's a very small surface, but I'm willing to allow it because it's vague enough that it isn't clearly improper, and because the result will be a lot of fun." Modify as appropriate, based on your judgement and your knowledge of your friends.

If that approach doesn't work, there is probably a fresh question to be asked regarding the social situation surrounding this.

Answer 2

I've been looking for clarification on this spell for a while as far as the surface vs object and this is what I've come up with.

You can place the glyph on the surface (outside) of an object, the Cover of a book, on a table, wall, or floor for example. You can also place it inside of an object, the pages of a book, in a dresser or table drawer, or inside a chest. Regardless of where it is cast it must stay stationary and will be dispelled if moved more than 10 feet from where it was cast. (Latest (10/24/2016) PHB 6th Printing/Errata)

Glyph of Warding was changed to say the following:

Glyph of Warding (p. 245). The first sentence clarifies that the magical effect needn’t be harmful. The final two sentences of the first paragraph now read as follows: “The glyph can cover an area no larger than 10 feet in diameter. If the surface or object is moved more than 10 feet from where you cast this spell, the glyph is broken, and the spell ends without being triggered” (6th printing).

This means that if you allow the player to use Glyph to power his "gun" then he must make his ammunition where he will be using it and can't take it more than 10 feet away from where he made it, by RAW.

As always it is DM's discretion to change the rules as he sees fit. Just make sure that your players don't have any big problems with the changes and have an understanding that any rules changes can be used by anyone, PC or NPC.

Answer 3

Surface is one of those terms that has no clear definition in regard to RAW and usually isn't stated explicitly. The extend of the area, whether it be a minute area on the back of a shell, the sunny place of the world (the ones the Dwarves refer to as surface) or the watery surface of a lake, depends on the context. A few examples:

PHB page 48, Unarmored Movement: [...] you gain the ability to move along vertical surfaces and across liquids [...].

Here, the authors clearly mean an area that is big enough for you, whether you be a dragon, giant, human, or pixie, to walk on.

PHB page 92, Hide In Plain Sight: [...] you can try by pressing yourself up to a solid surface, such as a tree or wall, that is at least as tall and wide as you are. [...]

Here the authors are more explicit and refer to your size to define the area but give examples of the nature of the surface.

PHB page 231, Demiplane: You create a shadowy door on a flat solid surface that you can see within range. The door is large enough to allow Medium creatures to pass through [...]

Here the dimensions of the area that is covered by the surface is given in the second sentence, at least medium sized.

In your case the matter could be easy if you were to go by what the description provides:

PHB page 245, 246, Glyph of Warding: [...] you inscribe the glyph [...] upon a surface (such as a table or a section of of floor or wall) or within an object that can be closed (such as a book, a scroll, or a treasure chest)[...].

Note: The caster can choose whether he wants to cast the spell either on a surface or on an object. It is their choice and not limited by the object itself. After all you could cast it on the first page of a book and state as trigger "opening the cover page".

The examples refer to some well-sized objects which you could use as a reference and simply rule that smaller surfaces cannot be inscribed. You could refer to the intricate nature of the pattern and the lack of ability to inscribe these patterns on the back of something as minute as a shell. Furthermore, there is a possibility characters (PC and NPC) can detect glyphs using the right tools.

Same spell description: The glyph is nearly invisible and requires a successful Intelligence (Investigation) check against your spell save DC to be found.

This would state that the glyph needs to be big enough to be seen. If characters were to start arguing that their glyph is especially small and requires a tougher DC, you could simply disallow it. Alternatively you could try to go the way of a good DM and allow it. However, you should then require characters make the necessary skill checks. Require a proficiency, for example, in Runecrafting and a hard DC to make them small.

To sum up: While everything hints to the glyphs needing to be large enough to be seen with an Investigation check (due to them being nearly invisible by magical means), you could allow players to craft tiny glyphs with the right tools, time, and proficiency. After all it would be rather neat to have a character become famous for his skills in exquisite and tiny rune/glyph crafting.

Answer 4

Rules about objects differ from those about surfaces, anyway, which may solve your immediate problem in a stroke.

In terms of size: A glyph is a written symbol. The surface must be large enough, flat enough and steady enough for the caster to write a complicated magical symbol whose effect depends on it being correctly drawn (even if no actual writing implements are used). It can be up to 10' in size.

If a player is trying to do this, I would first ask them to finger-paint their name legibly (or the word 'Glyph' if they have a long name) and see how small they can do it in the normal casting time.

If they're really interested in doing non-conforming glyphs, I might be willing to house-rule and trade some investment crafting skills and some additional restrictions in exchange for the ability to write glyphs on smaller surfaces. For portable objects, I'd consider that akin to crafting and look to balance the rules with that.