Variations of the visual appearance of a stained glass window during the course of the sun in the sky.
[Document in French] A timeline of the visual appreance of a stained-glass, in parallel the colors of the Sunlight and the colors of the Sky, during a sunny summer day.
(PC : click-droit > “ouvrir l’image dans un nouvel onglet” pour voir l’image en grand)
(right-click > “open image in a new tab” to zoom)
Simulation of the changing visual appearance of an East-oriented Stained-glass window depending on the daylight color and orientation:
7:30 AM: before the sun rises, the sky illuminates the window
7:45 AM: a yellow Sunlight reaches the window
8:00 AM: the Sunlight is already whiter
12:00 AM: the Sunlight is white
12:30 AM: the Sunlight disappears, only the sky illuminates the window
4:00 PM: idem
6:00 & 8:00 PM: the sky’s color changes slightly
All this has been simulated using physical data about the light of the Sun and the Sky in the south of France, and physical data acquired by scanning colored glass with a spectrophotometer.
With the studio Debongnie (http://vitraux-debongnie.be), we are working on a Stained-Glass prototype to be installed in a 13th Century Cistercian Abbey in the south of France. My project passed the pre-selection and we are in the final of the competition against 2 other duos artist/glass-studio.
Cistercians didn’t put colors, pictures or crosses on their windows. Their windows were supposedly « albae fiant, et sine crucibus et pricturis » (white – or colorless(?) -, and without cross and representations). Very few original 12 & 13th Century Cistercian windows survived and we know little about how they interpreted this rule.
My proposal is to produce “white light” in the Abbey, by a combination of different optical types and colors: transparent light greenish blue, light blue and light reddish blue mostly, and opalescent whites that diffuse light and are less transparent.
During the course of a sunny day, the light will vary. The visual appearance of the window will be changing a lot because of this variation.
Behind the window is a yellowish-white stone-wall. Before noon the window and the wall behind it are in the shadow. Around noon, the sun illuminates the window directly and the opal glass are becoming very bright. During the afternoon the wall behind becomes illuminated, allowing the transparent colors to appear. Finally around 4-5PM the shadow moves on the window and the opal glass stops being so bright.
GOLD + BLUE = WHITE LIGHT
Interestingly, opal glass will appear white but will project amber light on the walls or the floor of the building. The average color of the light passing through the window has been computed to be white. The glass selected last month in the factory Lamberts in Waldsassen were chosen to produce this effect, and the situation has been simulated with the light spectrum as measured last summer in the south of France.
BLUE SKY REVEALS THE COLORS
Finally, there’s the possibility of seeing the sky from an angle in the Abbey. When people will look at the window with the sky behind, it will reveal new colors again. What looked almost colorless will appear as different shades of blue and yellowish whites.
Finally, the glass version !
This is a stained glass element made with a traditional technique. The black lines are a combination of hand painted “grisaille” and lead.
I’ll soon describe the entire project in a longer post, stay tuned ;)
A paper model with “scanned” and calculated colors for the blue sky behind…
Below, the left one simulates a cloudy sky, the right one the blue sky
This is the design made by something like 5000 lines of code in Python 2.7 ;)
The first result of the algorithm
A & B & C : the raw material, pictures and glass transmission spectra (blue for different densities of the sheet, black for a reference white glass of the same factory)
In the previous post I showed some pictures produced by my technique of background removal for making “as accurate as possible” photos of glass sheets.
The photos were taken on a TL back-lighted, which is highly irregular. What you have to do is basically to multiply the picture A by the inverse of the picture B, after calibrating the pictures A & B together by making sure that their background has the same lightness. Of course you should do this in RAW linear 16bit!
This simple operation removes: the optical artefacts (the lens of the camera filters more light in the picture’s borders) the electronic ones (the CCD is slightly non-linear). It also automatically generates a “perfect” white balance, whatever your light source is… The only pity is that it adds some noise, but for our application this is fine.
I developed a method for selecting parts of the glass sheets based on their spectral transmission, by combining spectrophotometric measurements, math, and the corrected pictures :
The 3 zones A, B, C have an average difference of 14% in luminance when Blue-sky light passes through them.
other glass sheets characterized in the same way:
Graded Cobalt Blue light ref. G161, origin: Glasshütte Lamberts (Germany)
Graded Gold Pink pieces, origin: Glasshütte Lamberts (Germany)
Non-standard yellow ref. Special Yellow UV sample, origin: Glasshütte Lamberts (Germany)
Light Turquoise ref. 1242xx, origin: Glasshütte Lamberts (Germany)
Dull and relatively light Blue-Violet, ref. 1302F, origin: Glasshütte Lamberts (Germany)
When working with mouth-blown “Antique” glass (the glass traditionally used to make stained-glass), the irregularity of the material is a given property. Every sheet is unique and its thickness varies between 2 to 6-7 mm, with an average thickness of about 3 mm.
For perfectly transparent sheets, the color of the glass depends on the thickness of the material. If you want to have a high-level of control over the color that you want, a possibility is to measure the glass thickness using a digital camera and a light table.
However, this is not easy. The light-table non-uniformity has to be taken into account to correct the pictures, as I did here.
It’s been a few months that I’ve been developing software/hardware solutions to perfeclty measure the transmission of light that is characteristic of every single piece of mouth-blown glass. It now works pretty well.
(If ever you are interested by the technique you can leave a msg!)
19/04 — 28/05/2016
Note: from April 20 to 24, the gallery will be open from 10am to 6pm.
On white paper sheets, grids of little colored squares are painted. For every composition, the two juxtaposed colors are complementary and the proportion of each color is calculated for the optical average of the grid to be a grey. The local probability for a square of the grid to be of one or of the other color is determined by two superimposed sinusoidal waves, whose frequency and direction are randomly chosen. The complementary colors amplify themselves mutually when we look closely at them: a light yellow is more light and more yellow next to a dark blue-violet and vice-versa. However, the resulting color of the patterns is light, balanced, and a bit faded by the paper whiteness.
Because the colors of the compositions interact with each other and with the colors on the walls, the pieces were placed in a random order. There was no good reason for any of them to be next to another one in particular. The two colors used in every piece were used only once in the series. Some of them are very similar – for example the Pigment Yellow 74 and the Cadmium Yellow dark n°9 –, and these small differences are made more perceptible when they are next to each other. The variety of the colors used in the series covers all existing hues: red, orange, yellow, green, blue-green, turquoise, blue, blue-violet, violet and magenta. There is no black nor grey in use. The name of the pigments used and the order in which the compositions were produced determines the titles.
The wallpapers behind the frames and the drawings were generated by a similar algorithm that works with physical color measurements done with a spectrophotometer. Every pattern is unique by its shape and colors, but is generated by the same series of rules and constraints. 50% of the paper is covered by paint, and the superficy of the little squares can be 4 mm², 2 square root of 8 mm², 16 mm² or 2 square root of 32 mm².
“Soleil de minuit”, stained glass pannel n°5/14 (detail), 2016
LAST MINUTE INFORMATION: I’ll be the first speaker during the First Transatlantic Stained Glass Symposium, April 26,2016 – April 28,2016 in Waldsassen
Artist, independent researcher, color theory teacher at the national visual arts school La Cambre in Brussels, BE
Presentation: Between Tradition, the visual Arts and the digital technology: a digital stained glass project made of Lambert glass in a metro station in Montreal, CA
My art tries to be a visual equivalent of what music is in the field of audition. I reject every concept that doesn’t reflects in a material and visual reality.
For the last 8 years I develloped an approach centered around « light and color », that is based on a scientific methodology, on computer programming, on physics and color theory. Like a painter my tools are brushes, pigments, paints, paper or colored glass but also lamps, scientific instruments and equations. For me, the technique and the conceptual quality are two sides of the same problem, I wish to create a work that blurs existing categories such as « art », « science », « invention », and I defend the idea that scientific knowledge is free from the individuals that create it and from the institutions that fund it. Science can be used and practiced by anybody that understands it including outside of the academia and of the industry.
In 2015 I proposed the realization of a large-scale stained glass project in the frame of a competition involving an exchange of artworks between the cities of Brussels, BE, and Montreal, CA, and I won. I am currently working on the production of the artwork with the studio Debongnie in Belgium. The project consists of 14 stained glass pannels for a total of +-50 m², that have been completely designed by a computer algorithm. My software uses a spectral-colorimetric database of 350 different Lamberts glass samples measured in the factory with a spectrophotometer in the summer of 2015.
My talk will explain how I successfully adapted the techniques of color-management that I developped in my previous works to the medium of stained glass, what problems I encountered during the conception and the production of the pieces and how they were solved algorithmically or pragmatically in Debongnie’s studio.
The talk will be divided in 3 parts:
1- An explanation of why I wanted to work with stained glass in the context of my artistic work with light and color
2- « Soleil de minuit »: outlines of the stained-glass project for Montreal
3- The production of the stained glass in detail, from the physical color measurements to the conception of the algorithm, and to the material production in the studio Debongnie
I’ll conclude this presentation with a “hansei” (a japanese word meaning “self-reflection”, meaning to acknowledge one’s own mistake and to pledge improvement). I will criticize my own approach based on what I have learned by working with Lamberts and Debongnie and on what I’d like to change in my way of dealing with the medium of stained glass when I’ll have a chance to do it again.