If you like this post, and live in the Portland Oregon Area, consider taking my August Plein Air Workshop. (See right column.) It's the sort of stuff we learn about out in the field, and have fun while we do it.! - TJK
Just before I headed out the door for my second plein air painting festival of the year I received an excellent question from Sam, who follows my blog. Such a good a question I thought I'd offer it up here.
Sam, I'll try. But it will be a long and somewhat incomplete answer.
A sky is always a major thing for a landscape painter to grapple with, en plein air or in the studio. I can't (or won't) offer any hard and fast method to painting a blue sky other than tell you to go outside and look at it, but I will offer up a few guidelines to consider...
However, before I do I'd like to say that in general, unless your sky IS the focal point to your work, then it is probably better to find a way to subjugate it to other parts of the painting. If you look at the entire history of oil painting you will conclude that most of the great painters of any period gave us less sky in their compositions than we can encompass with our eyes. Partly because we have a wider frame of view than such painters were willing to contend with, and partly because those masters preferred to direct our attention to other things they felt more important.
But hey, to respond to Sam's actual question...
There are more things going on within a simple blue sky than meets the eye. And the kind of sky I am talking about is the clear unpolluted type that can present itself between mid-morning to late afternoon. (Sunset, dawn, dusk, and the effects of atmospheric particulates fall outside of what we will cover in this post.)
A boring monochromatic sky.
Only thing that changes is the value of a greenish-blue.
1. There is always a change in value from lighter to darker, from the horizon upwards. Most painters immediately get this. Not as much value shift as some artists like to portray, perhaps, but there is definitely a move from a lighter to darker value as we raise our eyes up from the horizon. (Until you start to approach the sun. Then it reverses from the glare.) The reason some experienced artists might darken a sky behind an object is to bump the contrast of that object, say a lady in a white dress (Monet) or the trunks of an aspen grove (me). A common trick, admittedly, but if it is taken to an extreme, or done sans finesse, can confuse the viewer into thinking they are looking at a night time painting.
A tri-Hued sky.
Same values used, but with modulated color.
It is subtle, but the red and green quotient in the blue begins to
interact in a manner a sky does in nature.
2. Within that modest value shift there is usually a shift in hue as well. (Actually, you can be confident that anytime you see a shift in value occurring outdoors there will also be some sort of shift in hue as well, but I digress. Another post...) Starting at the horizon, this shift in hue normally transitions from a greenish-blue to a reddish-blue as you move upwards. (Which explains why so many contemporary landscape painters use a cerulean with a cobalt or ultramarine blue in their skies.) How visible the shift is to the observer depends upon what time of day it is, and which direction he or she is facing. If the sun is out in front then the shift may be subtle. If the sun is behind you, the shift will be more apparent.
Same as the tri-Hued sky.
But now with some flickering Contrast of Color tossed in,
3. Then there is the optical effect that occurs within your own eyes. (Or to be more precise – within your eyes and brain!). The effect is an instance of Chevreul's Law of Contrast of Color. LCC essentially tells us that your eye/mind will introduce dissimilar hues into a field of blue we call a sky. You know what I mean. It is that vibration you experience when you look hard at the big blue yonder and it seems to shimmer with unidentifiable color. Believe it or not, it can be helpful to add that variation to the flat blue you see. Same value-hues, but slightly modulated patches of cool and warm (Cerulean/Cobalt, for example) versions of blue. All to excite the eye.
Way over the top Blue Chroma. Projecting out in front of the tree.
Some folks may like this image the best. But if they do,
I don't want to see the wall colors in their home.
4. If you lay in a sky using a blue which is more saturated than the rest of your picture then no matter what you attempt, it will never recede into the background space. Your sky will always appear to float in front of the rest of the image. This is due to how we perceive Chroma. If all other things remain the same, we usually perceive stronger hues to be closer to us than weaker ones. In fact, this (almost always) is true in reality as well, although I can think of a few exceptions I've come across when working outdoors. Difficult exceptions to contend with and requiring some artistic license to resolve.
So, in the end it is best to remember as we paint a sky that we are creating a fiction – an illusion of reality – and not try to slavishly copy what we think we see. As artists we hope to prompt a memory, elicit a strong emotion, and acknowledge the beauty we find in the world through paint. But we should not to attempt to mimetically recreate what we see. If we do we will fall short. Even the masters did. Paint has limits. Light itself does not.
So for me, a sky has a job to do. A role to play – which is most often to just hang out in the background as a supporting character. Not to behave like a spoiled and petulant diva who craves attention.
Oh, okay, Sam, since you emailed me your specific question about paint, here are a few things to consider...
a. Get rid of the thalo green. Don't use it. Too harsh and pervasive of a colorant and it will invade everything else on your palette. Use viridian instead. Real viridian. And Viridian 'Hue' is almost certain to contain thalo so don't use that either. Thalo is that colorant you just took off your palette, right?
b. Allow your skies to be grayer than you think. It's okay to have neutrals in a painting. They make the stronger color sing.
c. Intensity is less about what brand we use than whether or not the paint has enough colorant (pigment) to retain a sense of hue in the lighter values. So we should buy good paint, not the cheap student-grade stuff that turns out to be a false economy. This may be the cause of your graying. Too much filler and extenders. If there is much more than a colorant and drying oil in an oil paint then we should ask the manufacturer why. (There are some reasons why such additives are in the tube, but they are seldom there for you, the artist.)
d. If you do decide to mix in a little yellow at the horizon I suggest you use a cool yellow such Lemon Yellow (a shelf name, check the ASTM label for the actual pigment), or a Cadmium Yellow 'Light', as both are cooler forms of yellow and thus are more likely to mix cleaner into a light blue without turning dirty.
e. Luminosity results more from keeping our paint layer transparent or translucent than it does anything else. This means exploiting the white of the ground as much as possible and reducing the amount of white in your mixtures. Once we introduce white into our paint the game completely changes. Completely. Soccer turns to football. A topic for a future post, eh?
f. And finally, be aware that a sky don't alway shift towards the green along the horizon. (I know I said it does above.) Sometimes, under certain conditions, there will be a shift towards the pink, lavender, or orange instead. So try to verify what is actually there and don't assume. Don't depend upon what you believe is there, or what some photo says in there because photos are notorious for getting it wrong. The camera lies because it has to. If you find yourself having to depend upon a photographic reference then spend some time figuring out how you are being deceived. Because with a photo, you are being deceived . . .