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Tropes are storytelling devices. This series of articles on how to use or not use them in comics was first published in my Comics & Cartoons Weekly on deviantART.
"Exposition is a literary tool that is used to give information to the audience through dialogue, description, flashback or narrative." Source: tvtropes.org
Exposition is an essential part of many stories. It's almost inevitable that, at some point, some kind of critical info will have to be imparted, either to the reader or to the characters or both. This can be done in many ways. Skillful exposition will inform the reader without them noticing they are being filled in, but done poorly it can break the flow of the story. The worst thing you can do is an Information dump.
An infodump is an exposition sequence that is way too long, throws too much information at the reader in one go, and consequently stops the story completely for the duration. If it happens in the introduction, before the story even begins, then you're asking the reader to wade through a ton of material before they're even sure they really want to read the story! Very risky unless this is done in an attractive format. Star Trek came up with its Captain's Log for that, which presents the advantage of having the exposition done by the lead character and in a way that makes sense in context.
It's particularly easy to end up with infodumps in literature, where one can get carried away with the writing, but they can readily take place in comics, where they can take various forms:
• An endless conversation between two characters, which can result in a visually boring scene because nothing actually happens while they're talking. It's best not to have such a long dialog in the first place, but if inevitable, make sure to keep a visual interest by varying panel sizes, camera angles, perspective; have something interesting taking place in the background, close up on the characters' body language, etc.
• An "illustrated story" where the exposition takes the form of a sequence of vignettes with a narrative voice in a box. This is much less dynamic than comic narration and produces a feeling of distanciation to the narrative – which is exactly what is happening, as the characters themselves are distant from it. If it stretches across too many pages, the level of engagement drops enormously. Keep it short and visually amazing.
• A block of text, saving the trouble of drawing it all, and seemingly a painless way of getting the exposition out of the way – but in sequential art that stands out quite awkwardly. It's downright silly when the long speech issues from the mouth of a character who is in the middle of an action, for instance in the process of delivering a jump kick. Writer Chris Claremont is infamous for his absurdly long dialogues at times like this. Alan Moore on the other hand did pull off the text passages in Watchmen, where chapters are separated by pages of pure prose. In his case, they are not a pause from the story but an additional dimension to it, offering a mixture of new details and a different perspective on events already covered in the previous chapter (a curiosity catcher), taking place at points where the story has already paused and we're taking a deep breath before the next chapter.
If you find yourself committing an infodump, the first question to ask yourself is, "Do I need to explain all this at this point in the story?" You may be able to spread out the info along the story in smaller chunks, less noticeable and easier to digest. Perhaps you can simply use a lot less words and still convey what needs to be conveyed (think of this: if you were hanging out with someone and they asked you how something, how would you answer? Try this verbally and you'll find your answer tends to be much more concise than it would be in writing, because you have less time to think and you automatically select the most important bits.) Another possibility is for part of the information to be conveyed non-verbally, through things the character sees, body language, whatever is appropriate. As an example, let's say we have the following two panels of a boy talking about a date. Panel 1: "I had a date with Jenny." Panel 2: "She's dreamy! I'm so in love! I can still feel her lips on my cheek where she kissed me!" All of panel 2 is redundant. All you need is one panel of the boy saying "I had a date with Jenny", with a dreamy, soppy expression, fingers lightly touching a spot on his cheek, and you've said it all without needing to say it. No medium is as expressive as comics, and this expressiveness should be exploited to the full.
Now if you've examined your exposition and found that you really can't condense it or redistribute it, you need to consider ways of making it entertaining, to really suck the reader in. If you can't help the change in pacing, go all the way with it instead, making it a different experience through a change of style and/or medium as well. Parallel narrations can be very compelling if applicable, meaning that for the duration of the exposition you show both the current story and the backstory unfolding side by side, ideally in a way that there's a relation between the two at any given moment. Other than that, it's really all up to your creativity and having a good feel of how your story flows/what you can allow yourself to do with it. If you look closely at any comic or graphic novel that you consider to be good, you can probably spot within it well-done exposition to be learned from.
A specialized type of poor exposition is the Intro dump, where you introduce a truckload of characters in a very short space of time. Have you ever walked into a party and been introduced to 12 people in a row? You probably only remembered the first couple of names. A comic is no different. When a reader learns a new character's name, they also need to find out why this character is worth remembering before another one calls upon their attention. This isn't to say that you should start with just one character and wait several pages before daring to bring another one in, but do start small and introduce the rest at an organic pace. This insures that readers develop interest in each of them; this connection between reader and protagonists is highly desirable.
There are a few well-established devices used to make a character launch into an explanation. A favorite is to make a character arrive in the midst of a situation and ask: "What's going on?" Simple, but unquestionably natural.
But many devices are beginning to verge on caricatural by now and can almost only be used tongue-in-cheek, unless the writer gives them a new polish. This is the case of As You Know, where one character explains to another something they both know but the audience doesn't. If there is no good reason within the story for the characters to discuss whatever it is they both know, this sounds poor. In Scrubs, for instance, the presence of interns, which is perfectly normal, is conveniently used to make doctors explain procedures for the audience's benefit. In CSI on the other hand, the detectives keep explaining rudimentary forensics to each other for no good reason at all.
Also poor is the Postponed question – a characters asks a question that they would logically have asked a long time ago. It is only asked now because the viewer or reader needs to hear the answer now.
Captain Obvious, a character who is made to point out things that are already obvious to other characters as well as to the reader, is in definite disgrace by now. This trope was so rampant in Silver Age comic books that today instances of it are usually accompanied by another character responding "No kidding!" It was already rather noticed in the 70s, where an episode of Star Wars has Han Solo snap at C3PO: "I'm glad you're here to tell us these things!" Similarly dumb but surprisingly endurant is the habit of some superheroes to explain how their powers will protect them – undoubtedly for the benefit of new readers but completely maddening for everyone else. Cyclops: "Only my ruby-quartz visor can contain my optic blasts." Rogue: "Ah cain't touch another human bein', or mah powers'll absorb their thoughts and abilities." It almost sounds like they have a hard time remembering them doesn't it? How about this example, thought by Random while being blasted into a puddle: "What's happening? Mutant power to randomly deflect any other mutant power thrown at me isn't working!" *groan*
A character may be present whose raison d'être is to ask questions in the audience's place. This can be a child, a newcomer, someone with no expertise among a specialized crew, or even the Watson, named after Sherlock Holmes's chronicler, who was there to provide a bridge into the detective's mind. All these, when used wisely, make for smoother exposition than having a character who is a full-time Mr. Exposition, that is he (or she) exists solely to explain things to the protagonists, whether they really need the explanation or not.
Whatever you do, avoid Expospeak! This is the funny way in which characters often find themselves speaking when they're in the middle of an exposition. Suddenly they sound like they're reading an essay, which is exactly what their lines are, as the writer was so intent on the exposition s/he overlooked the fact people just don't speak that way. A simple way of avoiding this: read your dialogues out loud, or have them read to you. If it sounds unnatural, revise! People usually speak in shorter sentences than they write, using more familiar words, with a high likelihood of idiomatic expressions
As a final piece of advice I would add: Don't be afraid to not explain everything. Outside plot-essential points, there is nothing wrong with letting a reader wonder about things s/he sees in the world you're drawing. The sense of wonder comes from not having all the answers.