Channeling Winslow Homer

“I spent months trying to make my students see that the sky was seldom so blue as they painted it”.

John F. Carlson

I have a friend who went to Italy to paint with a group.  At the end of their stay everyone lined up the canvases they had done.  He was the only one to have different colored skies in each painting.    Why?  Because skies, if you actually look at them, vary, but we often depend on our visual memory where a schematic all-purpose blue is recorded .   Everyone knows that clouds come in many different shapes, but it may come as a surprise to you how much variation there is in the cloudless sky.  It varies from:

1. top to botton
2. left to right
3. time of day
4. day to day
5. season of the year
6. geographical location

Even if skies vary in real life, what’s the point of putting so much emphasis on a “minor” part of the landscape.  Well, because it ain’t minor.  Carlson in his seminal book on landscape painting (see below for reference) says that the sky is “the key to the landscape.”   You might begin by checking out the Cloud Appreciation Society here if you have never considered  skies much.   They have a wonderful guidebook called “the Cloudspotter’s Guide” which even includes a chapter on the Morning Glory Cloud that people travel to Australia to hang glide on, and an extensive photo gallery.

The idea, of course, for the artist is not to memorize what color to paint the sky in each of these situations.  However, with awareness of this incredible variety in mind, you should be motivated to take many good looks at the sky and not depend on your long-term visual memory in which the sky is always the same blue.  It’s probably safe to say, you’ll never see the same sky twice.

It’s best to start first with just a discussion about the “bare” sky and leave clouds for a separate discussion.

Getting a sense of luminosity in the sky

The land is always darker than the sky  and that value change gives the sky a sense of luminosity, shining over the land.   When there is a distant storm the values (dark sky, lighter land) are reversed and the land looks more luminous.   I think a luminous sky is noticeable when you get it right.  However, it’s somewhat tricky.

Basically a surface (in this case the sky) is considered “luminous” (that is glowing or emitting light not just reflecting it) when it is lighter in value than the value of a perceived white surface in the same lighting situation.  This white surface, in the case, would be on the land somewhere.  That means you have to be painting at least some of the land at the same time as the sky to judge values because the value of the sky can vary depending on conditions.  An overcast day lets less light through, and the land is, therefore, darker.  So ideally the color in the sky has to be lighter in value than the value of something white on the land.  Or to put it the other way around, the land part of a landscape has to be fairly dark in value compared to the sky –even in the case of passages that are supposed to read as white or light.

To have a luminous sky  all your landscape whites (and lights) have to be toned down a bit, not much but just a little bit.  Or put it this way, on the land you never want to have a pure white (except perhaps in the highlights).  With watercolor that means, of course, that on the land part of your landscape you never want to have the untouched paper showing.  In practice this may means just painting a relatively light value wash over the land at the outset and leaving the sky untouched paper which is often the suggestion of watercolor teachers.  This would allow lighter than white passages in the sky (meaning really lighter than how you paint white on the land) .

There are many painter who make it a rule to never use pure white paint right out of the tube, but to cut it a bit with another color like raw umber for example, and they often tone their whole canvas down at the outset.  Often they say this is to judge values better.  It is the same argument for not using a white palette since you can’t judge the values there either particularly if you are going to transfer the paint to a toned support (canvas or paper.)   The equivalent in watercolor of not using tube white in oil  is not to do what sometimes is called the “cheap workshop trick” of leaving paper untouched for the white.  However, I am beginning to suspect the reason for toning down whites lies in being able to make some parts of the painting luminous.

Think of this:  ”white” passages in the landscapes  look white even if they are in shadow, and in shadow they would be painted gray.   This is color or value constancy.  The eye adjusts its reading of the value or color of something to maintain it as it is in full light when it goes into shadow.    In the photograph two down from here there is a sky and a mountain with snow on it.  The snow looks pure white to us and therefore lighter than the blue sky, but that is not the case.  Even while we see the snow as white,  the sky looks luminous.  If you take a small tube like a short drinking straw and look at the snow in isolation,  it is actually darker than the blue of the sky.

In short, luminosity (some color theorists called it “brilliance”) means “whiter than white.”

The sky and the figure are luminous in Cole’s painting.  There is nothing as light in value in the land as the luminous sky and the luminous figure.  The figure really pops out against the dark background which probably also has something to do with simultaneous contrast, but it also looks luminous.   There are some spots of white flowers which are relatively insignificant and to my eye look grayer than  the pure white figure and the light sky.  The way to check this is to look at the reflection of the figure in the water to see a darker white and compare it to the white flowers nearby.  Both the reflection and most of the flowers seem to be about the same value, and this darker than the figure.

This luminosity is one of the reasons to look at skies and paint them with care although Cole pushes it a little too much for my modern taste.  However, without that sense of light coming from the sky a landscape can fail.  There are, of course, a lot of other clues to the light, for example shadows, but the sky is, perhaps, the most important.

This means that the sky can not be too blue (that is too intense, highly saturated) because it will also be too dark a value compared with the light passages in the land and therefore the sense of a luminous sky, the source of the light, will be lost.

The sky and the land interact by reflections

The separation of sky and land is not absolute.  There are little spots of sky reflection in the land, and, when we get to clouds, we will see that there are reflections of greenish land in the bottom of the clouds.

atmospheric perspective in the sky

The structure of the sky is a flattened dome.    At my height the horizon is about 3 miles away, but here is a website that will calculate it for your height.   When I am looking at the distant horizon, there is more air between me and a ship on the horizon that there is between me and a star overhead, and that is why the top of the sky is blue-violet.

(In art books it is commonly said that the top of the sky (the zenith) is closer than the horizon, but there is no actual place that can be called the zenith in the sense of the “end” of the sky.  The “Karman line” (100 km) is the height at which there is so little atmosphere that a plane cannot fly unless it is going fast enough to go into orbit.  It is where an “eronaut” (a pilot) becomes an astronaut!) and outer space begins.

All this means that there is atmospheric perspective with regard to the sky just as there is on the land.  In fact, Carlson (see below for reference) discusses the sky  not independently but as part of a discussion of atmospheric perspective in general.

changes in value in the cloudless sky

From a value point of view the zenith is darker than the distant horizon just like the nearby hills are darker than the distant mountains, and the sunny side of the sky (if there is one) is lighter in value than the opposite side.

Since value trumps hue, this version of the sky on some of the license plates from Maryland works because the value changes are pretty accurately descriptive of the sky.  On the other hand I doubt anyone has ever since a sky quite like this in terms of hue even in the state of Maryland.

changes in hue in the cloudless sky

By the same token the bands of color changes in the sky get smaller as they recede, that is as they get  closer to the horizon, just like houses would get smaller in the distance.  They would also become lighter in value and warmer (particularly if there is pollution, but also because the blue rays of light tend to be obstructed by having to get through more atmosphere).

The point is to visualize the sky not as hanging behind the landscape like an all blue curtain behind the action on a stage set, but as receding in space just as rest of the landscape does.  Thus it is subject to atmospheric effects just like the rest of the landscape.

Different hues in the sky

Although the sky is predominately “blue”, the undertones of the sky varies through the 6 different spectral colors of the rainbow.  The best way to see this yourself is to look at a sky that is mostly clouds but in which the cloud cover is broken by discrete openings in the clouds that reveal the sky.  If you’re lucky, you will find a sky that has these “sky holes”, a  term usually used for sky poking through trees.   You will be able to easily see that the “blue” of the sky is very different in both value and hue depending upon the height of the hole in the clouds through which you are viewing it.  (Of course, the lower holes will actually be farther away not lower. )

Photographs do not get all the colors in the sky because the software is mostly concerned with flesh colors, but the one above does have a few different hues.  One of the things the software does is to make the sky too blue, that is too saturated and dark compared to the land.

I think it helps if you train yourself to think of cyan as an independent color and not a variety of blue.   Many newer conceptualizations of “primary” colors make this distinction.   If you can really convince yourself of this, you will rarely see a one color sky because it will almost always been blue at the top and cyan lower down!

John F. Carlson in his Carlson’s Guild to Landscape Painting (see here) writes that the colors from zenith to horizon are basically like a rainbow (this is seen predominately in a bright, summer sky) :

1. violet blue
2. blue
3. greenish blue (cyan)
   
4. yellow-green
5. roseate gray  (alas with pollution this may be “extinct”)
   
6. a thick, milky, warm rosy gray which is darker than 5  (today, with pollution it is often brown in urban areas)

Remember that these bands of colors will not be the same size.  I’ve found that a thin line of violet blue at the top and a thin line of rose at the bottom look the most realistic to me.  In between there’s washes of blue and blue-green about the same size.  Then there’s some yellow-green.  I’ve found that, if I make the colors into discrete bands it doesn’t work at all.  In particular I tend to have the yellow-green only a partial band on a cloudless day.

The effect of the position of the sun

The reason a partial band of yellow-green seems to work is that there is not only recession backwards, there is the effect of the sun shining from one side or the other.  Most people do not paint the sun in their picture but they do portray the light of the sun as coming in from above and to one side.  That means that there is variation in the color of the sky from one side to the other.  I remember being taught, I think it was in high school actually, to make the upper left corner darker blue grading to a lighter blue in the right upper corner.  I was never told why.   I have read that the part of the sky nearer the sun is lighter and less intense  (saturated) compared to the part away from the sun.  I think it would also depend on the height of the sun in the sky.  If it were low in sky, I think the reverse would be the case.  It’s like lighting a model from the left.  Although the light is on the left, it falls on the right background, so the background is lighter on the side away from the light. In the case of a figure to portray light comes in from the right, the background has to be dark on the right and light on the left.  Of course, the model is lit just the opposite way.

why is the sky blue and cyan

Light travels through space in a straight line until it bumps into something in our atmosphere.    It can bump into relatively large particles of dust and water droplets or small gas molecules.   (In space where there are no particles to bump into the “sky” is black and the sun is white.)

dust and water droplets

When light hits these large particles, it gets  bounced off in different directions. The different colors of light are all reflected by the particle into which the light bumps. The reflected light appears white because it still contains all of the same colors.

gas molecules

When light hits a gas molecule, some of it  (that is certain wavelengths we see as a color) gets absorbed. After awhile, the molecule releases the light in many different directions.  The different wavelengths of light are absorbed differently. All of the colors can be absorbed, but the higher frequencies (blue and cyans) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering. (Rayleigh was and English physicist who figured this out in the 1820′s.)

When we look overhead at the sky we are seeing the scattered light that we read as blue and cyan.  When we look toward the horizon that blue and cyan light has been scattered out of the light already and we see what is left, the light that produces the warm colors.

types of skies

Carlson divided sky into three categories.

1. cloudless skies
2. overcast skies
3. dramatic skies which can be ominous in which earth-sky values merge into a “greenish-blue gloom.”

and I would add a forth category since “dramatic” skies are mostly tonal:

4.   colorful skies:  sunsets, sunrises, etc.

We have already talked about 1.

The completely overcast sky Carlson describes as a silver white mass or like looking at light coming through ground glass.  Such a sky allows less light to hit the land, and there is a greater value difference between sky and land.  The land is darker than a less cloudy day.

However, there are also slightly overcast skies in which there appears to be a haze, particularly in the distance (that is, “lower” in the sky) which can be quite yellow-gray.  Here Carlson’s rainbow of colors is much more prominent.   In fact, today as I write this is such a sky.  It’s morning in March and the sun is shining with long,  hard-edged shadows where I am, but the lower part of the distant sky is a bright, yellow-gray.

Tim Miller of Australia has a U-tube video of a slide show of his 365 daily paintings of the sunset in the same place from the same vantage point  here which you might enjoy.

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• sky blue