Glass-light interactions on the prototype


With the studio Debongnie (, 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.


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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.


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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.



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.


Picture of the first third of the window-prototype


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 ;)


glass prototype making

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Next week we’ll finally be able to judge the result.

Preview of prototype placed in-situ


probably not accurate, but it gives a first idea.

The list of unique shapes



Each unique shape that makes the map from the previous post. Total 173 unique shapes, 299 glass pieces.

The map!


the map of the stained-glass

This is really the result of intense work during 4 1/2 months. More news soon.

Printing the map

Simulation of “Opal” glass


Opal glass is a strange material. It is a colorless glass that scatters blue light in the same way the earth’s atmosphere does it with sunlight: the sky is blue because blue sunlight doesn’t travels straight in large thicknesses of air, but in every directions. The sun appears yellowish because of the same reason: the blue part of the sun’s light spectrum has partly vanished from its rays under the form of blue sky.

In the opal glass, a very thin layer of diffusive “milky” glass containing very tiny particles is plated (“plaqué”) on the glass. Opaque white “flashed-glass” and opal “flashed-glass” are exactly the same material, but on the opaque version the layer of milky glass is very thick, up to 1 mm, while it can be maybe a 100 times thinner on very light opal glass.

It is very difficult to simulate the color of this glass on the computer: on the light table you see nothing but what seems to be a “cloudy” or “hazed” white glass. You need some distance to see the color appear, you need the light rays to pass in straight lines through  the glass otherwise the color won’t appear.

I did some research and I arrived to some pretty good results. The numbers under the pictures indirectly refer to the thickness of the milky layer. The left color is the one that appears by light transmission, the right one by light scattering.

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When the layer gets really thick, transmission becomes zero and the glass is opaque and white.


It’s really “white” but the light passign through it becomes yellow-brown.


…working on a Stained-Glass prototype


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 ;)



Serious glass sheet optical anatomy


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:



Photographic Glass Characterization


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!)



Quasicrystalline Stained Glass prototype

quasicristal glass prototype

First test for a new algorithmic glass project, more information might come at the end of the year 2016. Prototype made with 6mm and 8mm lead & float glass by Studio Debongnie:

algorithm square detect

Expo Solstice (Post-industrial Animism, June 21st), picture

adrien lucca vitrail solstice

Fragment (decommissioned), 2016

Laminated Antique mouthblown Glass


SOLSTICE flyer fr-1SOLSTICE flyer fr-2

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