Pehr Sällström
TRANSPARENCY AND WHITENESS
A study of colour appearances in connection with transparent media
in comparison with ordinary surface colours.
Version date 2023-06-12
Video at https://youtu.be/KhnRGoVGg3k
Ludwig Wittgenstein notes, in his "Bemerkungen über die Farben" (1951), some enigmatic facts, concerning how we experience -- or in any case how we speak about and characterize -- colours. For instance he asks:
How does it come that something transparent can be green, but not white?
Hm …Let's find an answer by playing puppet-theatre with colour samples!
SCENE 1 : SHARP SCENE LIGHTING
Here comes the first actor: a blue card. In the sharp light from a distant lamp it casts a black shadow on the white wall.
A second blue actor enters the scene. Like the first one, it casts a distinct shadow, but -- this shadow is blue! The actor consists of a transparent material. It has a dual role - both in casting a shadow and in lighting it up. We see that the first actor is blue, because it reflects the light falling on it. We also see that the second actor is blue, but in this case because we see the white wall through it.
Now the scene changes - the wall behind becomes totally black. You still see the first actor, but the transparent one becomes invisible. The colours, it contributed, disappear.
Next, the first actor is exchanged with a white one. As concerns the blue actor, observe that where you catch a glimpse of its shadow through it, there appears a deeper blue colour.
We push the two actors closely together - and a sculpture of remarkable complexity results. One can distinguish seven areas of different colour. Plus the white background. Take your time to find out how we get so many areas of different colours!
Again, with black background only two areas remain visible. Namely, the white actor, and as partly seen through the transparent one.
From this we learn that a coloured transparent medium on top of a white ground may look as a surface colour. The white ground is both illuminated and seen through the transparent layer. Hence the resulting surface colour is deeper than the colour of the transparent layer itself.
SCENE 2 : DIFFUSE SCENE LIGHTING
In diffuse lighting there are no shadows and from a distance you cannot distinguish transparent samples from opaque ones. Make a guess here!
Now I change to black background - and the two cards with surface colours stand out.
A transparent actor needs something light behind, in order to be visible. Look here:
Four actors standing in a row, aginst black background. A transparent one passes by in front of them. Its colour fuses with that of the one behind, occationally bringing forth a new colour. Against the yellow one: green, against orange: brown, against the magenta one: violet an agains the white one: light blue.
Suppose I should ask, what is the colour of the actor itself? The answer would be: Lightblue. The way it looks against white. The white surface is passive, it doesn't itself contribute to the mixture, but displays the actors own colour.
*
Against a multicoloured background transparency and depth are readily perceived.
Vi look through the blue sheet on a part of the scenery behind ... and holding the sheet closer to the eye we see the whole scenery as in a blueish light.
Goethe, in his Farbenlehre, describes how the mood of the scenery changes, when you look at a landscape through coloured glasses.
Instead of being seen as an object among others, the transparent plate now contributes by modulating the illumination of the scene.
*
However, to come to grips with the issue: Why is it that a transparent medium may have any colour, except white? Let us once more compare transparent media and opaque surface colours.
All colour materials, transparent as well as opaque ones, have one thing in common: They bring with them an element of darkness. The transparent plate doesn't only contribute hue but, as we have previously seen, also throws shadow.
A transparent plate must not necessarily be green, blue or orange - it may also be simply grey. Our question - why it cannot be white - accordingly doesn't concern the attribute hue.
Look wha happens when the contribution of darkness is diminished. The greyscale ends up with pure white and the transparent one with clear transparency. No darkening of what is seen through it.
So, in the world of transparent colours this is what corresponds to white, in the world of surface colours.
Together, against white background, they are seductively similar. What they have in common is that both represent the world before colour - that is to say before darkness became involved.
It would be logical to call a clear glass-plate "white". As when we speak of "white light", meaning colourless light.
However, Wittgenstein pointed out that the very concept of transparency presupposes three-dimensional space. There must be something behind that can be seen through the transparent medium.
We started our investigation with two blue actors on the scene. Here we see two colourless actors, in the same scene. We now see that the two actors are radically different, after all.
Even the glassplate throws a shadow because its plane surface acts as a mirror, reflecting away a small amount of the incident light, creating a mirror image of the light source.
Transparency and whiteness. From the point of view of colour systematics they may be closely related -- but at the same time we are dealing with extremes. This is the paradox Wittgenstein wanted to draw our attention to.
Scen 3 – THE DISTINCTIVE CHARACTER OF WHITE
There is no compromize in the choice between transparency and whiteness. Look at this half-transparent plate. What colour does it have? You may call it white, or whiteish, if necessary to give it a colourname. To get really white it must grow denser, until it reaches full opacity. On the other hand, to be acceptable as purely transparent, it must become completely clear, without any hint of whiteness.
When we are pondering the unique properties of white, it is no longer as a colour among others. Not as a material, that can be bought in a paint-shop. No, it is the whiteness itself we are trying to grasp.
*
The white surface has an important role to play in connection with light, space and vision. Let me give you a hint about it.
To begin with. The difference in apperance between the transparent and the surface colour may be described as a difference in attitude. Look here:
The surface colour manifests itself as autonomous, independent, dominant.
The transparent one is heteronomous, it relates to the situation, is drawn into the community of colours present, and mixes with them, even until no longer recognizable.
May even show us the whole scenery in coloured illumination - as here in orange light.
A surface colour, as the one to the right, manifests itself by stopping the gaze. You cannot see what is behind and it doesn't matter.
Now, compare with the white surface! It also stops the gaze, but not as provocatively. It is as if it wanted to be transparent for our gaze - showing us something else than itself.
The white surface is tabula rasa, it invites something, whatever, to be displayed on it. A shadow-projection, a drawing, a painting...
Listen to Kandinsky, characterizing white in "Über das Geistige in der Kunst":
Weiss ist wie ein Symbol einer Welt, wo alle Farben, als materielle Eigenschaften und Substanzen, verschwunden sind. (.. ) Deswegen wirkt auch das Weiss auf unsere Psyche als ein grosses Schweigen. (…) Es ist ein Schweigen, welches nicht tot ist, sondern voll Möglichkeiten.
*
Both the white and the transparent material are essentially associated with light and space.
A room with white walls creates a soft presence of light, suitable for complicated visual tasks.We human beings are inclined to stay on "our" side of the white wall and take pleasure in the world of pictures and artefacts, we are capable of producing ourselves. In short: we feel at home in the comfortable world "whitness" can give shelter to.
The transparent window glass, which lets in the light we need, is also something through which we can look out into the world on the other side of the wall. Letting the gaze travel all the way to the horaizon and ultimately, like Galilei with his telescope, to the dark space of universe, with its enigmatic glimmering configurations.
EPILOG
Johann Wolfgang von Goethe had the intention to put together a "Farbenlehre", presenting an overview of what we know about colour in nature, how it appears under various conditions - with special regard to the painter´s ambition to make reasonanble representations of natural scenes, with the help of mixtures of available paints and pigments.
In one of his drafts he started by considering the nature of white and black colour materials. A fresh snow-field was, for him, a striking example of whiteness:
Pure water crystallised to snow appears white, for the transparence of the separate parts makes no transparent whole. (…) The accidentally opaque state of a pure transparent substance might be called white; thus pounded glass appears as a white powder.
As always, he pointed to a natural phenomen that could lead us to deeper insight. In this case the fact that water is transparent, whereas in the shape of millions of snow-flakes it can present us with a non-transparent white surface. A remarcable connnection between transparency and whiteness!
Maybe, the fragments of broken glass are still transparent themselves, but with plane surfaces reflecting light in arbitrary directions, thereby scattering the incident light and making it omnipresent in the room.
We humans of today are obsessed by the idea of perfection. The perfectly plane and homogeneous glass plate is a technical masterpiece, as is perfectly diffusing white surfaces, with as close to 100% reflection of incident light energy as possible. But the reality of practical life is always "both-and", or "neither-nor" as the case my be. Ambiguous, elusive and above all: with inexhaustible nuances.
Goethe, as the realistic man he was, suspected that the intermediate case -- a semi-transparent material -- could give us a clue to further important optical phenomena.
He soon found that as soon as a material is not perfectly transparent it shows a tendency to hue. So, with regard to Wittgenstein's remark, one would say that, yes, transparent materials are usually more or less coloured. Hueless transparency as well as a perfect white surface are ideal extremes.
This observation takes us in first hand to optical phenomena on the sky. Such as the reddening of the setting sun, the blue of the sky or distant hills. Rainbows and coronae. What Goethe classified as "physical colours", unlike the "chemical colours", based on selective absorption of radiation, to-days excursion has mainly dealt with.
NOTES TO THE SET-UP AND PRESENTATION
The scene is arranged as follows:
We have the back of the stage. A wall: white, black or with a picture. In front of it the actors. Relatively far away we have the observer ( or camera) and a concentrated light source (in this case a projector halogene lamp 12v, 100w).
Observe the symmetry. For instance, a transparent coloured glass plate can be positioned in front of the observer or in front of the lamp - i both cases presenting the scene in coloured illumination.
In the case of diffuse lighting, the lamp is shut off and we have general room illumination from the window, on the right side.
The point with using a mini-theatre with physical colour samples as actors, is to avoid the illusory depth of 2-dimensional pictures. Here we are dealing with real physical depth and real transparency.
Furthermore the identity of the actors is important. Each one has its "own" colour, its own surface reflectance, respectively transparency. We are observing them in various spatial constellations, and in various kinds of illumination. In this world so called "subtractive mixing" is important (creating darkness), as it is for any painter. In the world of projections on white surfaces (or the computer screen) we are ealing with "additive mixing", leading to increasing lightness.
There is a lighting condition, not presented in the video version. Namely spotlight on the back wall:
With room illumination and spotlight on the white background.
No room illumination, only spotlight.The roles have changed. The surface colour is invisible (black) whereas the transparent actor, with its colour, is seen.
*
A physical, optical analysis of the situation can be done from the point of view of the observer (in terms of "sight rays") or from the standpoint of the light source ("light rays"). The sight rays, starting at the observers eye, can be used to calculate where the sight is free, among opaque objects. A light ray emanates from the source, hits a point on the object surface and is reflected to the entrance pupil of the eye of the observer, where it contributes to build a projected optical image on the retina. Observe that we (as observers) do not see these light rays, entering the eye. Nor do we see the retinal image. They belong to the organ and the processes by help of which we see when directing our intention and visual attention towards the outer world.
The analogue between the eye and a photographic camera is only partly relevant. The camera doesn't see. Here I agree with James Gibson's "ecological optics" and the discussion he carries through in his books.
*
An investigation, like this one, based on what can be elucidated by help of a theatrical scene with colour actors, is deliberately bound to the world of things, spatially delimited objects with distinct shape.
Our flat actors are simplified representatives of ordinary spatial entities. An ordinary material object has "volume colour" and this is not so easily made invisible by using a black ground. See this example:
Transparency, as such, is not located in space, as is our transparent plate. The transparency of space itself is simply just the case - a matter of fact. We become aware of it through being able to see things over there, far away.
But even the white surface has this indeterminacy in its spatial location. Especially when filling the whole field of view, without any sharp boundaries. As when you stand close to the white wall in one of the artist James Turrell's Ganzfeld installations.
The white clouds on the blue sky seem well shaped - until you flies into them. Then they are more like shapeless mist.
*
REFERENCES
1)
Wittgenstein
Wie kommt es, dass etwas Durchsichtiges grün, aber nicht weiss sein kann? (I:19)
Durchsichtigkeit und Spiegeln gibt es nur i der Tiefendimension eines Gesichtsbilds.
Der Eindruch des durchsichtigen Mediums ist der, dass etwas hinter dem Medium liegt.
Vollkommene Einfärbigkeit des Gesichtsbilds kann nicht durchsichtig sein.
Why is it that something can be transparent green but not transparent white?
Transparency and reflections exist only in the dimension of depth of a visual image.
The impression that the transparent medium makes is that something lies behind the medium. If the visual image is thoroughly monochromatic it cannot be transparent. (I:19)
So far Ludwig Wittgenstein i ”Remarks on Colour” / Bemerkungen über die Farben, del 1, Cambridge March 1951
It must be admitted, I used Wittgensteins question as an excuse to present my little study of colour appearance in situations comprising light + material media + observer.
A more straight-forward answer to the question (I:19) could be: There are no coloured transparent media. They are transparent only in so far as that shapes, based on contrast, can be clearly seen through them, but - as we have seen - colours are more or less distorted. Only the colourless plate can be called really transparent.
From a physical point of view one would say: a coloured medium may be transparent for certain wavelenghts of light and more or less opaque for others. There is an ambiguity in the term "transparent" as Wittgenstein uses it when formulating his "riddle".
2) Jonathan Westphal
is one of the many philosophers who have felt challenged, by Wittgensteins remarks, to more or less far fetched intellectual elaborations. (Which is exactly what Wittgenstein himself was careful to avoid - finding comfort in the attitude of "an innocent child"; inspired by Goethe's straight-forward approach to colour.)
Anyway Westphal treats the remark (I:19) extensively elaborating around the concept of white. He honestly admits (quote) "I hope that the answer which I give to Wittgenstein's puzzle question is a clear one, even if it is misguided and I have not understood the point of the question as Wittgenstein means it."
It however seems to me that he essentially arrives at the same conclusions as I do in the present essay.
J. Westphal. Colour: A Philosophical Introduction. Aristotelian Society Series Volume 7. (1987, 1991)
3) Goethe
says that snow ”uns einen vollkommenen und unzerstörlichen Begriff des Weissen gibt”.
He points out that White has to important functions:
§7 Das Weisse hat die grösste Empfindlichkeit gegen das Licht.
§8 Der mindeste Strich, der mindeste Flecken wird auf dem Weissen bemerkt. Alles, was nicht weiss ist, zeigt sich im Augenblicke auf dem Weissen, und es bleibt also der Probierstein für alle übrigen Farben und Schattierungen.
Versuch die Elemente der Farbenlehre zu entdecken (1793) Leopoldiner Ausgabe (1951) Band 3, p 190-192
In his Entwurf einer Farbenlehre (1810), Goethe discusses similar phenomena to those I exemplify in my video-essay. They are treated in the chapter on "Chemische Farben":
Ableitung des Weissen §494, 495; Erregung der Farbe (Trübe effect) 502, 517; Mischung, scheinbare 567, 568; Lasuren 571; Mitteilung, wirkliche 573, 581, 582, 583; Alles Lebendige 586; Entziehung 594, 596; Mineralien 615;
4) Kandinsky
White is a symbol of a world from which all colour, as a material quality and substance, has disappeared.
For this reason, white affects us with the absoluteness of a great silence.
It is not a dead silence but one full of possibilities.
Das Weiss ist wie ein Symbol einer Welt, wo alle Farben, als materielle Eigenschaften und Substanzen, verschwunden sind. (...) Deswegen wirkt auch das Weiss auf unsere Psyche als ein grosses Schweigen, welches für uns absolut ist. (...) Es ist ein Schweigen, welches nicht tot ist, sondern voll Möglichkeiten.
Über das Geistige in der Kunst 1910 ( Benteli Verlag, Bern 1965 - p 96)
English translation by Hilla Rebay for the Guggenheim foundation ed. 1946
samt i översättning av Ulf Linde: Om det andliga i konsten (Vinga press 1994)
5) James Gibson
The important thing with Gibson is that he has incorporated ideas from systems theory, information theory and pattern recognition in his approach to perception. Elaborated in his first monograph: "The Senses Considered as Perceptual Systems" (1966). Perception is an ongoing explorative activity, leading to a more variegated knowledge of the objects of study. For him, three-dimensional physical space and its contents is what visual perception is dealing with. Directly: not via two-dimensional so called "visual images" of the world. (Which is the shortcoming of most psychological experimental studies of perception!)
Another important consequence of this processual view is that our colour vision need not be delimited to three qualitative attributes, with reference to the three sorts of light sensitive cones in the retina. What we regard as "the colour of an object" is rather something we arrive at through aquaintance, by seeing it in various kinds of illumination and together with various other objects.
Se bl.a. The Ecological Approach to Visual Perception, Boston 1979