In this
lesson we're studying water vapour in the form of simple steam clouds. It
shares some similarities with fire and smoke, both of which you've had a
chance to experience in previous articles. Simple steam is a very useful
effect in 2D animation, from a common teacup scene to a cloudy, winter
breath effect.
It's also highly effective when used with subtlety and you'll see in the treatment section that the most effective steam scene can even be one where you see very little steam at all!
Steam is rising clouds of hot water vapour that become less visible as they cool and disperse. In cool air, especially in certain lighting conditions, the individual particles are easily visible to the naked eye. One great way to observe steam is by having a well-lit cup of tea with a dark background behind it. The dark background allows you to clearly see the brightly lit particles.
In the stunning video below, you can start to appreciate the complexity of this beautiful effect.
Just as you learned with smoke and dust introductions, particles allow us to see otherwise invisible turbulence. The case is no different with steam so there is particle movement, density and dispersion behaviours that describe the various features, currents and zones of a steam cloud. Looking at the source of a typical coffee cup steam effect, the particles may be initially fast and directional. However, they soon appear to float on sheets of warm air and as they're lifted and tossed, we see more cloudy and turbulent shapes.
Simply considering the temperature difference between your scene and and the steaming element is enough to put you ahead. For example, let's say your scene has a character sipping a cup of tea indoors, by the fire. Steam would be very subtle here. However, if the same tea was outdoors in a dark, snowy night, the steam might be stronger. The difference between tea and air is the key to how subtle or strong the steam appears.
Of course, all this depends on the lighting as well. Teacup steam is more obvious when lit, but very soft in shadow.
Fig. 1 - A hot cup of tea in a warm room gives off less steam than when it's in cold air.
The teacup type of steam shares some design similarities with the incense smoke we did in lesson 0103. It has smooth sides at first, which rise up and become clouds. However the big difference is dissipation. While smoke remains visible, hangs and drifts in the air for long periods of time, steam dissipates almost suddenly. Even slow steam can be a remarkably brief effect, with shapes spiralling into nothingness before they've had a really good chance to be seen.
In the image below, we see some standard animation steam behaviour. Starting from the source, the particles rise and merge together, almost like a thinning of the "trunk". Particles twist and roll upward on convection currents where pieces may break away as the cloud cools and spreads. Finally, as the heat is lost, those broken pieces dissipate quickly.
Fig. 2 - From the source, upwards to dissipation
Because of its real-life complexity, steam is vastly simplified in 2D animation. That said, we can understand the steam effect better if we break it down into a few zones marking the particle stages.
Fig. 3 (right) shows 4 simple stages or zones of steam.
The classic cartoony ribbon style of coffee cup steam can be very poorly done. See if you can avoid the cheap back-and-forth wiggly band and instead, try for a nicely designed effect with varying widths and serpentine curves.
Fig. 4 - Left: very cheap, kinda ugly ribbon steam and, Right: nicely varied design
Cloudy steam is ideal for a winter's breath. Just like dust though, avoid the popcorn effect! Keep your shapes moving, and keep them varied and interesting.
Fig. 5 - cloudy steam
Steam doesn't have to be a roaring column shooting upwards at a constant speed. The designs below are a very low-key style of steam and, once animated carefully with some subtle treatment, it'll be a really nice scene.
Fig. 6 - low key, simple designs that are in fact, more realistic
You may also notice that parts of the steam are shaded. This is the "behind" steam that you can treat differently with double-opacity or other treatment. Don't be afraid to let the steam (or smoke or fire) wrap around itself in this way. It's a nice touch and looks great when treated.
Controlling it - Because of how quickly it naturally dissipates, steam can be easily confined to an area without making it appear contrived. For example if a character is sitting with a steaming bowl of soup, the director may ask you to avoid animating any steam in front of the character's face. Because of the speed that it dissipates, steam is very forgiving and it can be designed in such a way that it avoids an area without appearing too forced.
Steam can, at times, move very much like a cloudy fire, though obviously it's slower to dissipate and nowhere near as hot. This means it'll have a lot more turbulence and gradual shape changes, than a fire scene. Just like fire, everything starts at the source and rises! Avoid moving any shapes downwards or you'll ruin the effect.
In the video below, I'm animating a low key teacup scene in the pose-to-pose method, which is ideal for keying out your steam shapes, then getting the timing right before inbetweening.
When the source is travelling, for example a character carrying a steaming bowl of soup, the steam trail is constantly being broken up. The broken pieces must continue to rise, even though their dissipation will be fast. Some forward momentum is also nice, to give the feeling that the steam is being pulled along in the turbulence of the character.
Fig. 7 - Travelling steam. As pieces break off they continue to rise, but slow down and dissipate as they continue to move forward in the direction of travel.
Hot steam rises into the air and resolves fairly painlessly. Cold steam as in Fig. 8, is something else though, the difference being that it falls, rather than rises. For example, a container of dry ice, or perhaps a mad scientist's test tube of crazy bubbling stuff. In this style, the falling steam may need to interact with objects below it, like floor, table, hand, etc.
Regardless, the principles are the same, with the initial gathering before spreading and dissipating (see also Fig. 3).
Watch any steam and you'll see that just like fire, the hotter part of the column pulls inward, almost like the trunk of a tree (see Fig 3, zone 2). This is what flame and smoke do, too. With steam though, after this initial gathering inward, the cloud spreads and broken pieces may drift off at odd directions. Sometimes it's nice to put one or two of these little rogues into a long scene, but don't force them into every scene. They should be special, appearing rarely.
Lazy steam is best suited to a cozy environment and it can be a relaxing effect to watch. Fast steam on the other hand could be used to set a more active or lively mood. We'll look at steam jets in another article, but consider the mood difference between a gently steaming cup of tea and a rapidly boiling pot of broth.
Relative to the overall effect, steam dissipation can be quite sudden. You can animate a steam cloud upwards with fairly consistent density and volume. Once a piece breaks off, however, it disappears within just a few frames.
Experiment with different ways of dissipation. You can break pieces off, then shrink them into dots within 6-8 frames, but also try some splitting, spiralling or thinning dissipation. The more dissipation types you add, the better the scene will look.
Considering what you learned on previous articles, there is nothing really to say here about cycling the effect, except to reiterate that cycles should be as long as you can make them to avoid mechanical repetition, especially in long scenes. The longer the scene, the longer the cycle should be.
If you have a very long scene (AND the luxury of time and/or creative control) there's an excellent method of cycling that involves animating several different cycles of varying lengths and speeds. Suppose you animate 3 different cycles for the same cup of tea and refer to them as cycles 1, 2, and 3. You play those cycles in random sequence on the teacup, for example: 1, 3, 2, 3, 3, 1, 1, 1, 3, 2, 1, 2, 3, 1, 3, 2.
Multicycling is useful in a HUGE range of effects. Try it out with ripples, fire, smoke and just about anything else.
You may remember the cloudy fire style from the lesson on torch fire. What's interesting is that if we treat this fire with steam treatment (example at left), it's not half bad, if a little fast for a teacup! Steam has a lot of fire-like qualities and vice-versa. Just like fire, the more depth you can put in transparent objects, the better the scene will look.
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Steam is usually white, which means it contrasts best against a dark background. If your scene takes place in the snow, have you considered that the steam may not be visible unless it's carefully composed to show off the steam? Unless it's a crazy colour, is incredibly dense, casting heavy shadows, or there's something dark in the scene to serve as a backdrop for the steam, you could possibly recommend to your director that any steam simply won't be seen!
Before you start your steam scene, it's a good idea to be aware of the final scene colours and lighting. It may be that you spend hours animating the best steam in the world, only to find that you can't see it in the scene.
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Fig. 10 - 2 steam cycles, layered for depth
In Fig. 10, there are two layers of steam, which is usually enough to give some depth to any steam scene. You can even duplicate the same steam cycle, and use it for your second layer. Ideally though, you'd create a new cycle, perhaps with a "core" of steam to animate behind the main layer.
Blur will be used a lot in Steam animation but as much as possible, you'd ideally use directional rather than radial blurs. Even better is variable blur, which allows you to precisely control which specific parts of the cloud are sharp and which are blurred.
Using a mask or cutter to create negative spaces from dust, smoke or steam clouds is a method I personally developed for my own needs. If your steam is a scene-stealer, or you just want to give it something special that nobody else even considers, try it for yourself. It adds a whole lot of control that you don't get with single-layer stuff.
Treating your steam with some light effects, filters or modules will add another layer of amazingness. This also goes for dust, smoke, fog and so on. Assuming the steam is white, then you could consider a subtle offset shadow effect. If it's a coloured steam (e.g. chemicals, fumes) perhaps a rim-light effect to give it some roundness. (More on lighting effects in the next lesson).
For subtle steam you can use a ribbon or cloud style, or a combination of both, but it works best with layers. You may have barely visible steam clouds, but if they're varied in their movement, treatment and design, they will be seen and appreciated for their subtlety. Don't get vain and make the steam too obvious for the sake of showing off your drawings.
Steam needn't always be subtle. Sometimes you just have to make it obvious that the broth is viciously hot. Subtlety takes practice, but the treatment for scene-stealing steam is much easier.
Where you would normally push steam back until its barely visible, you can take an opportunity to show off.
Easy - As shown in the Design section, Figure 4, design and animate a steam effect loop from a teacup. Unlike ribbon smoke, steam should dissipate in some way, whether by fading or fragmenting.
Intermediate - Animate a blast of steam escaping an air pressure line, or a kettle. The high pressure steam is direct and straight, until it hits the air where it swirls, cools and dissipates quickly.
Advanced - As demonstrated in video 2, animate a subtle steam effect cycle of your choice with multiple layers that twist and fragment toward dissipation. If you choose falling steam, have it spread across a surface as it fades.
Whatever the design, steam is an effect that can be used in a wide range of interesting situations. This has been just a taste of fairly simple steam which, I'm sure you'll agree, can be quite difficult in its own right.
As we've been doing all along, the main idea is to start on small-scale versions of these effects, looking at their basics, then later applying them to larger scale. The next time we look at this effect, it'll be jets of steam that shoot out from things like steampunk robot joints and train whistles.
