This tutorial will work best for digital painting or traditional painting with oils. It may work for acrylics as well, but I don't personally use them, so I won't vouch for it. This tutorial assumes, for the purpose of digital painting, that you have a pressure-sensitive graphics tablet, such as a WACOM. If you're using oils, I'm assuming you have at least a basic grasp of common oil-painting terms and techniques. This probably isn't a good tutorial to use if it's your very first painting.
1. ROUGH PAINTING
The first thing to do is paint in the sky, itself. Background first, then foreground - in this case, the sky is going to be the background, and the clouds the foreground. So, we have to make a decision at this point: What sort of mood is this picture going to convey? It may be tempting for beginners just to glob on the blue paint (or do the Photoshop Fill tool equivalent), but the sky isn't always blue (true, it probably isn't quite the colours I've chosen, either, but this isn't a photorealism tutorial). At any rate, I've decided on a wistful, contemplative feel for this piece, so I'm going to use a pale coral as the base colour.
Notice that the sky is not one flat colour, though, even where the base colour shines through. I have used a 'wash' of the complementary colour (a greenish shade, since the coral of the background is red-based) to bring out the main tone. So the first step is to pick not only a main 'base' colour, but also to pick out several shades of its complementary, and a few darker tones of the main colour, as well. Put swatches of these colours in a separate file (or globs of them on your palette, if you're painting with oils) so you can refer to them easily later.
Since this is the planning stage, now would also be a good time to decide what direction your light will be coming from. You'll need to remember this later.
2. PAINTING, ERASING, SMUDGING
Now that you've picked your colours, it's time to start painting. An important note for digital painters, to start with: If you want a 'natural media' look, don't use the Fill tool. Paint the background in with the Paintbrush, manually, using a large, hard-edged brush, and multiple stroke-directions. Depending on the effect you're going for, the procedure will vary a bit here, but this is how I've done it.
First off, I set the foreground colour to the 'base' colour, and the background to a dark golden green. Then, I set the Paintbrush pressure-sensitivity options (Photoshop 5.5) to Size and Color. Having done that, I scribbled in the sky, making sure I varied the 'brushstroke' direction and pressure, so that I would get variations in hue and stroke size. When I paint with oils, I simply don't clean the brush after I finish with the first colour, and I keep alternating between the main colour and its complementary hues, using mostly the main colour to begin with, then laying in larger areas of the complementary depending on where the light is coming from.
If you're looking at the image above, you'll see three labeled circles, each with lines protruding out of it. Those are the brushes I used. Note that they're all hard-edged at this stage, and also that there's no Airbrush. At the moment, generalities are important, and colour. Not smoothness or perfection.
So far, we've used the Paintbrush. The Eraser will be used on the next layer. So, make a new layer at this point. Choose darker variants of your base and complementary colours, and use the Paintbrush to scribble in a great ugly full-opacity blob where you want the darkest parts of the sky to be. That's right--a great, manky, formless, hideous, 'What the HELL is that doing there?' blob. You oil painters aren't exempt from this stage, either. Go on - add the blob. You know you want to. Don't be scared - this is the fun part. Oils are great - you can paint right over that later. You can even rub it off while it's still wet. There are no irreparable mistakes.
Now, Photoshop users, get a big fat Eraser brush - about the size of the one pictured here, and start rubbing the blob out. Use horizontal, vertical, and diagonal strokes. Don't worry too much about nice, soft edges right now - we'll get to that later. Oil painters, get a clean brush with just a bit of the base colour on it, and start scrubbing over, around, and into that blob until is starts to look like it belongs in the sky. Add as many light washes over it as you need.
Do the same for the lightest areas - big light blob, rub it out, repeat till satisfied.
The next step is almost identical for both Photoshop and oil paint users. Take a small brush, and scribble with a snakey motion along any hard demarcation lines. (This'll be the Smudge tool you're using, in Photoshop.) This will give you a soft edge without sacrificing texture.
These directions sound very easy, but you may have to mess around and experiment for quite a long time to get it right, especially if this is your first try. But don't give up. Both oil painting and Photoshop are very forgiving media. You can even delete the 'blob' layers in Photoshop and try again if you think you've messed up beyond repair. (You can't, though. Mess up beyond repair, that is. I recommend not deleting, but keeping on going, painting over and erasing, instead.)
3. DRAWING CLOUDS
Okay. This is the part you've been waiting for. The clouds. And, really, if you've come this far, then the clouds will be very easy. The first thing to remember, no matter what medium you're using (EXCEPT watercolour, but this tutorial has NOTHING to do with watercolour) - Do. Not. Use. White. This is very important, so I will say it one more time. No white. Rather, the thing to do is block in the clouds in a very general way - just shapes for now, using very light colours, but not white! I have included the brushes I used for this stage in Photoshop - nothing fancy. This stage should take less than a minute to do, assuming you've already planned where the clouds are going to fall.
If you have not done this before, you should be looking at some cloud photographs at this point. It's important to remember that clouds, like any other object, have mass. The top of a cloud is different from the bottom of a cloud. I drew the clouds that happened to be outside my window while I was drawing this, with a few minor alterations. Reference is a GOOD thing.
If you're painting in oils, just use any large brush for this stage. Don't get into fine little details. Use washes for some areas of the edges of clouds, as I've used soft brushes in Photoshop, but leave some hard edges, too. Clouds have hard edges, as seen from the ground.
All right--we've got several steps in one, here. Start at the top of the picture. If you've been dying to break out Photoshop's Airbrush tool, now is the time to do it.
Don't go crazy, though--I've just added a couple of misty trails of cirrus clouds near the top of the picture, and made the edge of the top cloud a little less distinct. If you're using oils, of course, you're not going to run and get an Airbrush at this point. Just use washes.
Moving down to the next stage. This is where we add the shadows. Remember how we darkened and lightened the sky, with big, messy blobs of colour? Well, it's blob time again. I used a dark blue-gray, and a medium reddish-gray. If you're spending a lot of time with this, you might want to experiment with 'ambient' colours, as well. For instance, if your cloud is hanging low over a volcano, try painting some bright reds on the undersides of your clouds, as reflected light. I've just used lighter blues and reds for my reflected light, since there's nothing particular in the background apart from the sky.
This is also the time to firm up edges and contours, which is done with light and shadow. Remember the lighting direction you chose right at the beginning? Make sure you stick with it, or you'll get a very confused result.
In the final stage, I have added highlights - note that they are NOT white, although they may appear so on some monitors. This is very important if you're planning on printing your digital work, because pure whites areas don't look good on any but the very highest quality print. And even then, they just aren't very interesting. So unless you're going for a very sharp, graphic feel, leave the white out of it. Leave the highlights quite hard-edged - light often reflects quite starkly on clouds. So you don't need to soften up the edges too much here.
5. FINISHING THE PICTURE
Well, looks like you're done, in fact. The image above is more of an enlargement, to show some of the more detailed brushwork, than an actual step. All that's left to do now is...
...the foreground:) But that's another story... - I hope this was a useful tutorial for you.
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