Alicia Sánchez and Luis Castelo, The Application of Colour Management to a Photographic Record for the Conservation of Scientific Collections: Anatomical Wax Models, e-conservation Journal 5, 2017
Available online 15 March 2017
The Application of Colour Management to a Photographic Record for the Conservation of Scientific Collections: Anatomical Wax Models
Alicia Sánchez and Luis Castelo
During the 18th and 19th centuries, collections of anatomical wax models awoke great expectations for various cultural contexts and contributed towards the implementation of a new teaching strategy for the important medical and veterinary schools across Europe. The Complutense University of Madrid has two exceptional collections of this kind, one of human and another of animal anatomy, dating back to the Royal College of Surgery of San Carlos. Before proceeding with the proposed intervention of a cultural object or asset, it is essential to conduct visual tests on these to accurately determine their means of construction and condition. One of the most common tools used for the first visual study is digital photography. This article describes the working procedure employed for the photographic record of each sculpture. An artificial scaled wax model of a horse has been selected as a representative case study. In order to obtain an accurate reproduction of the piece, lighting, photographic record and colour management patterns have been established.
The role and importance of the Royal College of Surgery of San Carlos scientific collections rests upon the unique nature of the objects they contain. At the time of their creation (18th and 19th centuries), the anatomical wax models took on a truly technical revolution. The wax allows for the reproduced anatomical specimens to take on a high degree of accuracy and extreme realism, not only in terms of imitating the textures of every tissue or organ, but also in terms of its chromaticity. Although the artisans took great efforts to ensure the accuracy of the figurative representation, both the passage of time along with the adverse exhibition conditions and the natural aging processes of the materials have caused significant aesthetic alterations from the original intention and role of these objects.
The wax collection at the Complutense Veterinary Museum is comprised of 45 pieces, most of which dedicated to equine anatomy. The collection dates back to 1793 with the establishment of the first Veterinary School in Madrid, imitating the Alfort Veterinary School in Paris where they exhibited the artificial models made from various types of materials (wax, papier-mâché, polychrome plaster, etc.) and used by the teaching staff. Various historical changes, along with successive moves and changes of location of the pieces up until their current whereabouts at the University City of Madrid, opened in 1968. In addition to this, the changes brought about by technological advances and the consequent replacement of these items by other artefacts more appropriate for teaching ultimately contributed to their removal from the classroom to later be stored under unsuitable conditions for their conservation.
Photography is an extremely valuable tool for the documentation of a work of art or scientific object or artefacts, as it records an image of the piece in terms of the specific manufacturing techniques, as well as sequencing and contrasting their varying stages of condition, in order to establish the most appropriate intervention protocol, should it be required . Nonetheless, in order to achieve this goal, it is necessary that the resulting photographic image depicts the absolute likeness of the original . And in this sense, several methods for the capture and processing based on quality control are required to grant the photography any value as a scientific document. Nowadays, the systematic use of digital devices for taking images requires us to consider the use of equipment that ensures colour validity and consistency. The inclusion of standard colour casts during the photo shoot is essential if we are to guarantee accuracy.
2. 1. Optimum Equipment Configuration
The widespread use of digital photography since the 1990s has led to changes of the protocols for the use of digital equipment, along with the emergence of distinct workflows employed during photochemical photography.
This study on the registry of anatomical wax pieces will establish the optimum configuration for the devices. There are already photographic record protocols. However, for the most part, these concern the reproduction of flat art as a photographic record for their storage, such as the case of Metamorfoze of the National Library of the Netherlands [1-2].
Three key configurations that affect the resulting image and its quality and that must be adjusted are: a) Adobe RGB (1998) Color Space; b) RAW Files at Maximum Resolution; c) White Balance (WB).
Many cameras come with pre-defined default for sRGB space, however, the Adobe RGB colour space (1998) is much richer and more appropriate than the former (Figure 1). Moreover, the majority of digital cameras only have these two options. This configuration, among other options, allows us to first see an image on the camera screen that is much closer to that as later seen on a computer screen.
On the other hand, a RAW file contains all the raw data from the sensor and all of our camera settings as metadata. This means that a RAW file may be processed in various manners, on the basis of the needs of the image, which makes this a very versatile file. The downside is that every camera manufacturer has developed its own encoding and, therefore, we have just as many types of RAW files as camera manufacturers out in the market.
In short, we will configure our camera to gather a RAW file at its highest resolution, so that after it is processed we may obtain an image with the highest possible quality. Additionally, we will convert our native RAW file (CR2, NEF, etc.) with the image where we have incorporated the ColorChecker Passport casts on an Adobe DNG file, in order to obtain a camera profile (Figure 2).
Also, the default setting will allow us to correct any dominant colours that may be present in the picture, by balancing the colour channels of the image. This requires a custom WB to be made on a white or light grey patch, as found on the ColorChecker cast with a reflectance of 60% and free of any dominant colour. The classic Kodak grey card or any white paper sheet are both unsuitable for this procedure, as both have some blue cast that negatively influences this measurement . To the left of figure 3, the cast reading can be seen without the WB being corrected with the polarising filters placed on the light sources and on the camera, along with the unbalanced RGB values (185,192,187), as well as the histogram where a displacement of the green channel can be appreciated; and to the right, the reading of the now corrected WB, where the RGB values are balanced (189, 189, 189), along with the histogram.
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2.2. Displaying Correctly in Digital
Traditional working methods, based on the use of negative films or slides, are unsuitable when working with digital sensors. Currently, photometer is a very useful tool to calculate the correct exposure. On the one hand, although they are still calibrated to produce a correct result with film, photometers are still calibrated for scenes that reflect 18% of the light . On the other hand, the histogram, apart from being able to instantly view the resulting image on our screen, provides for an immediate comparison. The purpose of obtaining the correct exposure is to capture the maximum tonal range, allowing for our camera sensor from avoiding both over-exposure, whereby we lose information, and as under-exposure, where we find the greatest source of electronic noise.
2.3. Use and Interpretation of the Histogram of a Photograph
A good histogram must gather the broadest tonal scale possible, and for such it must be more or less centred on the graph. But not all photographs must provide us with this type of histogram.
When properly exposing the picture, the technique of exposing to the right (or ETTR) is required, in other words, slightly increasing the exposure by moving to the right of the histogram without going to beyond the end values (255) and then proceeding under develop with the editing software. This concept first appeared in articles of the Luminous Landscape journal by Michael Reichmann [4, 5].
The type of material (wax models) being photographed of determined the use of a non-incandescent source (tungsten or quartz), due to the high amount of heat they emit. On the other hand, such continuous sources can be currently replaced with more efficient sources such as LED or fluorescent lights. Despite fluorescent lights have a much more limited spectral range than inscandescent lights, are no less aggressive of them.
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3. The Used Lighting
The use of flash for conservation procedures has always been a concern due to the emission of UV light. However, we are talking about extremely low emissions that are negligible. Thomson is quoted as saying: “The continuous electronic flash is less harmful than continuous exposure under incandescent lights” . Although the equipment is cumbersome and expensive, it presents some interesting advantages such as they do not produce heat, the amount of emitted light allows work to be conducted with almost closed diaphragms and fast shutter speeds, the flash colour temperature is day light (5,500 K) and they are very versatile.
3.2. Fluorescent Light
Two 4 x 55 w Tred Fluo Dimmer panels were used and calibrated for daylight (5,500K). These sources were used without any accessories and also with polarised lights and camera. This kind of source produce soft light and they do not produce heat. However, they are heavy. They require the use of a tripod during the photo session since the light output is low. Before being used, they require a certain amount of time to warm up until the gas inside the bulbs acquires an adequate temperature for their optimum performance
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3.3. LED Light
Two 36 w 34 x 38 cm Nanguang CN-600CSA panels with a CRI index of 95 were used. The colour temperature is adjustable by 300 points for cold light and 300 points for warm light, between 3,200K and 5,600K. A total of 5,280 lux were produced at a distance of one meter. Led light has lightweight design, dont produce heat and allow adjustable colour temperature and intensity. Also produces soft light and can be used without the need of mains electricity, by using batteries.
3.4. Ultraviolet Fluorescence Photography
Portable Wood lamps (365 nm) were used. UV radiation can indicate the state of the conservation of the original materials as well as those added afterwards, for the diagnosis of museum collections. When an object is subjected to this radiation, its materials depict a very different appearance than the usual . The ability of a particular substance to fluoresce depends on the composition of the material, the degree of aging and the type of UV light wavelength chosen [7, 8]. A visual examination using UV fluorescence allows the curator or restorer to deepen the analysis and diagnosis of the object, verify the degree of deterioration and to detect any earlier restorations. This kind of light provides a distinctive image of the illuminated objects, therefore, allowing us to expose aspects that would otherwise be invisible to the naked eye. In the other hand the amount of light emitted is very low, difficult to measure and to focus, so exposure tests are required. The estimation of exposure, focus and WB are empirically performed through different tests that are measured in situ on the camera screen.
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4. Colour Management
For colour management, we attempted to maintain and reproduce the same colour aspect among the various processes and devices used throughout a workflow, as they reproduce colour in a distinct manner. What we aimed for was the colour to be predictable and repeatable. For this purpose, we needed to measure its behaviour and keep these measurements in a specific format that could then be applied afterwards: colour profile. In fact, the Adobe RGB 1998 space has become the standard in the sphere of photography and graphic arts as it maintains a quite good correlation between what we see on a high-end monitor and what our output device is capable of reproducing [9, 10].
5. Digital Photo Development
All the images were originally saved in RAW format, then processed using Adobe Lightroom 5.7 and finally a few parameters were adjusted in Photoshop CS6. Using Lightroom, the resulting camera profiles were applied using ColorChecker and any differences were compared before and after applying the profile for each type of lighting used.
6. Case Study: Anatomical Wax Model of a Horse
6.1. Historical data
The anatomical horse model used for this study dates from the early 19th century. Archival sources attribute the piece to the modeller Pedro Pablo Osorio, trained at the Royal College of Surgery of San Carlos, in Madrid, and to the anatomist Cristóbal Garrigó. This is undoubtedly a unique piece of great cultural value, registered historically during the age of comparative anatomy and in connection with the evolution of veterinary medicine.
6.2. Formal description
This piece represents a reduced scale equid (45 x 13 x 40 cm). As for the construction of the piece, it is a hollow sculpture in the round, created from a paste composed mainly of white beeswax, Venetian turpentine and lard, to which pigments were added to colour it and accurately represent each of the anatomical parts. The artificial model has glass eyes and the interior is fitted with small metal rods that coincide with the legs of the animal in order for it to be anchored to a wooden base that serves as support.
7.1. Visual test: comparison with different types of visible light and ultraviolet fluorescence
The anatomical model under study has suffered various kinds of deterioration due to its improper conservation over time. Most of the damage has been caused both by external agents (contaminants), handling of the piece by unqualified personnel (loss of bulk material, cracks and fractures in the most fragile parts that bear most of the sculpture’s weight), as well as the natural aging process of the original materials (crazing over the covering film, micro-cracks, voids and bubbles found in the wax paste used as the sculptural medium, colour changes, etc.). In order to record all this information, general photographs and detailed photographs were taken using diffused light, raking light and ultraviolet fluorescence. Aspects that have been taken into consideration during the visual examination of the anatomical model were:
a) Study of the anatomical detail
Colour channels for locating the anatomical part were used selectively. In turn, these images have served as a support tool for the development of digital mapping and deterioration maps.
- Orange: the anatomical details of the arteries were of secondary importance, in order to give priority to the thorough observation of the work undertaken for the representation of the musculature of the horse, which is most likely made from beeswax with additive and red pigments. It is also possible to clearly visualise the areas of the model where the creator has applied an undyed beeswax paste.
- Red: the entire body of the horse had been converted into a grayscale in order to facilitate the exact location of the arteries that are probably made with vermilion pigment or fine carmine, according waxwork technique.
- Yellow: the overall image of the horse has been retained in grey scale to emphasise the anatomical parts that have used undyed beeswax paste, as seen in the photograph as a yellowish hue.
b) Tooling Marks
It has been observed how the modeller used various utensils depending on the anatomical part being represented:
- Forked bone sticks to apply the dyed paste used to simulating arteries, vessels or nerves.
- Wooden flatteners for the wax paste intended to represent membranes.
- Iron tipped polishers for various finishes to smooth out parts of the sculpture and also to make a striated mark.
- Awl shaped or rounded iron soldering irons to join different layers of wax paste.
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c) Construction Imperfections
Although going completely unnoticed under diffused light, there are numerous air bubbles can be seen in the paste wax, especially in the parts that coincide with the striated sections. It is possible that this deterioration is due to an inadequate manufacturing technique. This information is of great interest and should be taken into consideration for any future restoration interventions.
d) Grime Deposits
The surface of the piece entirely covered with two deposited layers, one adhering to the wax paste and the other in suspension. The raking light and UV fluorescence imagery further emphasise the presence of dust particles embedded inside the recessed portions of the striated areas.
e) Deterioration of covering film
The study using UV fluorescence in combination with polarised light has facilitated the observation of a fine crazing that has formed over the covering film due to the loss of its mechanical strength during the natural aging process of the natural resin, and it has also assisted in the better observation of several existing abrasions on various parts of the model.
f) Mechanical damage
There are numerous fractures, especially around the area of the legs, particularly those surrounding the parts supporting the total weight of the sculpture. Additionally, it has been observed that by adding metallic elements in its interior, these have been subject to greater stress than the rest, which could have contributed to the appearance of microcracks and the loss of bulk material.
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The anatomical wax models were made for a wide range of purposes, such as the study of anatomy at art academies or medicine and veterinary schools, as an alternative to performing a dissection, and even public education. They have influenced scientific developments, being optimal support for resolving disputes between professional colleagues and also transformed the perception of the nature of the physical body. These models had come into use, not only to as a learning aid, but to satisfy the need to analyse. Ultimately, they are a refined synthesis between science and art, whose study provides an interesting and insightful connection between the history of science and the production of art.
With a few simple tools and a precise methodology, digital photography may be used to record details pertaining to these types of artefacts, thus converting it into an instrument for the preservation of scientific collections. The application of procedures and protocols ensuring reliable colour management, the use of lighting techniques such as polarised light, raking light and the use of fluorescence allow, through a controlled process, allows for the gathering of valuable information, thus enabling a thorough study on the photographed pieces. It has been intended to have established a simple protocol for anyone who has a basic knowledge of photography.
This study forms part of the results achieved under the scope of the R&D Research Project ref.: HAR 2013-42460: Veterinary Waxworks: documentation, characterisation of materials and methods for conservation and restoration at the Complutense collection, funded by the Ministry of Economy and Competitiveness.
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Alicia Sánchez Ortiz
Full Professor. Complutense University of Madrid
Luis Castelo Sardina
Full Professor. Complutense University of Madrid