A facsimile of the Wedding at Cana by Paolo Veronese
In the autumn of 2006, the Musée du Louvre reached an agreement with Fondazione Giorgio Cini and granted Factum Arte access to record Veronese's great painting les Noces De Cana. The conditions were carefully specified: the recording must be completely non-contact, all equipment must meet the highest conservation specifications and be approved by Veritas, no external lighting or scaffolding could be used, work could only happen when the museum was closed and no equipment could be left in the room when the public was present. In defining each condition the safety of the painting (and the other paintings in the room) was always the definitive factor.
In response to these conditions the logistical problems of recording a painting of 67.29 square meters were studied in depth. The conclusion was that we needed to develop a scanning system that could record at actual size and at the highest possible resolution within the limitations of both time and budget. In response, Factum Arte built a non-contact colour scanning system that uses a large format CCD and integrated LED lights. The scanning system records at a scale of 1:1 at a maximum resolution of 1200 dpi. The scanning unit is mounted onto a precision built telescopic mast. The telescopic mast is operated by an air-pump and can accurately position the scanning unit on the vertical axis. It has a maximum reach of 8 meters from the ground. It is fitted with a linear guide to position the scanning head in front of the painting. It has an ultra-sonic distance sensor to ensure that the scanning head is a uniform distance from the painting and is always positioned parallel to the picture surface. This is essential to ensure that each file can be merged together without scale, focus or perspective distortion. The scanning takes place at 8cm from the surface of the painting.
The scanning head moves over the surface illuminating the area that is being recorded. LED light contains no ultraviolet rays and generates minimum heat. The painting was scanned in 37 columns and 43 rows. Each capture was 22 x 30.5cm with an overlap 4cm on the horizontal dimension and 7cm on the vertical dimension. Each file was saved in 2 formats (Tiff and Jpeg).
The recording was done at 600 dpi with 16 bit depth of colour. During the recording of "Les Noces de Cana" 1,591 individual files were saved in Tiff format resulting in an archive of 400 gigabytes.
The telescopic mast was also used for conventional photography - using a Phase One H25 digital back fitted to a medium format Hasselblad body. The Phase One records 5488x4145 pixels (22 megapixel) with a pixel size of 9x9microns and 48 bit colour (16 bit per channel). The photography was done in 450 sections (18 columns and 25 rows) using the ambient light in the room.
The archive of photographic data consists of 593 different files intotal 41 gigabytes of data. -In order to cross check the information the painting was also recorded using a Nikon D80 producing an archive of 8.5 gigabytes of data-.
The lower part of the painting was recorded using a 3D scanning system made by NUB 3D (Spain). Factum Arte´s approach to 3D scanning is completely non-contact. No markers, spheres or registration systems are fixed to the object. The average working distance is about a meter away from the surface being recorded.
NUB 3D Triple White Light Scanning System uses a mix of optical technology, 3D topometry and digital image processing to extract 3D coordinates from the surface of an object. This technique, known as structured white light triangulation, produces accurate measurements of the surface by analysing the deformation caused when lines and patterns of light are projected onto the surface of an object. Multiple images are captured by an integrated camera in the measuring head and using these images the system's integrated technology calculates a co-ordinated X, Y, Z point cloud relating to the surface of the object.
About ten sq meters of the painting were recorded in 3D at a resolution of between 400 and 700 microns. The scanning was done in sections of one meter square generating an archive of about 1 gigabyte.
Some notes on the colour matching
During the recording extensive colour notes were made using a series of colour sticks made on site and matched to specific points on the surface of the painting. These were fixed into a book containing a 1:1 scale line drawing of the painting. A bit of the colour stick was cut off and fixed into the book at the corresponding point on the painting.
Colour is one of the least understood and most complex subjects. In the production of a facsimile you are seldom dealing with a standard flat colour. Most coloured materials age in complex ways - some of the most important are the changes in transparency revealing or obscuring the layered nature of the paint. Complex changes in texture result in an irregular surface complete with shadows and highlights and an uneven surface reflectivity.
Stitching the scanner Data
The first task, carried out while working in the Musée du Louvre was to pre-assemble all the columns using Photoshop Scripting. This resulted in a roughly assembled image of the entire painting. The final assembly, carried out in Madrid, was to reduce the 1,591 individual files into larger units accurately joined together. The vertical columns were used as the basic unit and each scan was accurately assembled into strips comprised of 8 or 9 scans. Each full column is made of 5 of these files. The file size of each unit is about 1 gigabyte. 185 of these units make the whole painting (with overlaps).
Due to amount of digital data it was impossible to work on the entire painting so it was essential to break it down into manageable units (file size under 12 gigabytes) with an accurate reference to each adjoining unit. Once these units were finalized the individual scans were flattened. The painting was then divided into 1 x 2 meter blocks - these blocks are the printing units. There are 44 printing units.
At this stage we are only interested in the accurate merging of all the units into an accurate map of the whole painting. The scanner data is in colour but no colour correction is done until the colour and scan data has been aligned. The colour data was recorded to give the maximum dynamic range allowing flexibility for the modifications to the colour and tone that need to be made before printing. For printing the scanner data is down-sampled to 300 dpi. At this resolution the assembled scan data consists of 9.7 billion pixels. The file size is 31 gigabytes.
Merging the colour photography and the scanner data.
The scanner data and the colour photographic data have to be treated independently but aligned in perfect registration. The photographic data (recorded in 16 bit depth of colour per channel in RGB) then has to be mapped onto the basic scanner data unit of 1 x 2 meters. The scanner data contains no distortion but the camera data always contains some lens and perspective distortion. The task of joining these two distinct types of information together is painstaking and meticulous.
There are between 12 and 18 photographs per 1 x 2 meter file.
Colour printing is difficult using only one data set but when more than one is used the problems increase exponentially. Factum Arte works with the Russian photographer Boris Savelev on all issues relating to the accurate printing of colour and tone. The solutions that were worked out to manage the colour printing of Véronèse's masterpiece are the result of a twelve year collaboration between Adam Lowe and Boris Savelev and required both lateral thinking and extensive testing.
The aim of the colour adjustments was to match the colours of an image printed onto gesso using Factum Arte's flatbed printer to the colour sticks recorded in the Musée du Louvre.
Once the initial tests were complete the panel at the bottom left of the painting was printed at actual size and further changes were made until both the tone and the colour of the two layers printed together matched the colour sticks, after the print had been varnished. Every change was archived and then simplified gradually resulting in a series of Photoshop 'actions'. One set of actions was applied to the Phase One data and another to the Cana Scanner data. Once finalized, these actions were applied to all 44 printing files and small versions of each file were printed. During the recording the lighting conditions for the photography and the scanning were kept constant so these universal actions resulted in accurate colour matching across all parts of the 67 sq meter canvas.
Once the two files had been corrected, they were printed in two layers, one on top of the other, beginning with the Phase One file. The photo data is printed with a richness of colour and a brightness that looks very photographic. The overprinting with the scanner data adds complexity to the tone and produces an image that does not feel like a photograph. When this is mixed with the actual texture on the canvas the illusion, even from close up, is of a painted surface and not of a print. After varnishing, and the final hand-finishing to control of the relief of the paint the illusion is enhanced even further.
Printing the facsimile
The facsimile was printed on Factum Arte´s purpose-built flatbed printer. This was built by Factum Arte's engineer Dwight Perry and is based on an Epson Pro 9600 digital printer. The printer uses pigment inks in seven colours (cyan, light cyan, magenta, light magenta, yellow, black and light black). The bed is fixed and the print heads move up and down the bed on linear guides. The movement of the heads is accurate to a few microns. The height of the heads can be adjusted during printing. This enables the image to be printed onto gesso coated canvas in pigment.
Rafa Rachewsky preparing the panels to be printed
Due to its history "Les Noces de Cana" has a complex and unusual surface. Each piece of canvas is coated with a layer of animal glue, a layer of gesso and fibre and then two layers of gesso. A pin registration system is used to accurately locate the print on the prepared canvas. Each panel is printed twice in perfect register. The first layer to be printed is the information recorded on the Phase One H25. The second layer is the scanner data. Both have been colour corrected prior to printing. The printed panels are varnished with a satin Golden acrylic varnish with UVLS, an ultra-violet filter.
Assembling the printed image
Ten 20mm thick Alucore panels were made. Each panel is 340 x 205.2 cm. When perfectly aligned in two rows of five panels they make up the whole painting. Each of the large aluminium panels is assembled from six printed panels with some of the panel overlapping the edges. First the printed panels are laid out on the surface and perfectly aligned. They are then spliced together with irregular cuts that follow features in the painting. Straight lives are always avoided. The canvas is then fixed to the aluminium with PVA and weighted down while drying. The joins resulting from the stitching of the printed panels, are then retouched by hand by a team of trained conservators. The joins are first filled with a mixture of Golden acrylic moulding paste and glass microspheres. When the join has been carefully filled it is first tinted and then retouched using Golden acrylic paint. During this process a gloss Golden varnish is used. A Golden gel is then used for the final texture and to enhance selected brushmarks. A final coat of satin Golden varnish with UVLS is applied.
The honeycomb aluminium panels, with the retouched printing, were sent to Venice in sections and then fixed on site to an aluminium frame. This was done in two parts and lifted into place. The final control of the surface was done when the facsimile was in its final position and with the lighting that exists in the refectory.
The small joins were filled with Acrylic gesso mixed with glass balls to reduce the shrinkage.
The Painting was recorded between November and December 2006 while in situ in the Musée de Louvre. All aspects of the production of the facsimile were done in Factum Arte's workshops in Madrid between January and August 2007
"Digital miracle restores water and wine masterpiece to monastery"
The Times (15/11/2007)
"El milagro de la reproducción. Venecia vuelve a poseer "Las bodas de Caná", de Veronés, gracias a la tecnología digital" (The miracle of reproduction. Venice retrieves the "Wedding at Cana" thanks to digital technology)
"As the Italian government steps up its battle to win back looted antiquities from museums around the world, a Venice cultural foundation has chosen an alternative and high-technology path to retrieving a lost 16th-century masterpiece with the help of a British artist and some cutting-edge scanning equipment"
"Il Veronese riprodotto, una svolta per l'arte" (Veronese reproduced. A turning point in art.)
"The facsimile, by the Madrid enterprise Factum Arte, is a stunningly accurate replica of the 732-square-foot canvas. Details are reproduced down to the most minute topography, including the raised seams rejoining the panels that Napoleon's troops cut the painting into when they transported it to France in 1797."