Conservation : Physiochemistry of the objects

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  • Conservation

    Physiochemistry of the objects

    The museum as a meeting-place may be considered from either the objective or the subjective point of view, according as to whether the emphasis is placed on the social sciences or on the exact sciences of physics and chemistry. To deal with the problem, a combination of elements from both these fields of knowledge should be employed.

    The objects in museums may be divided into three groups: (a) real things created by man or by nature and possessing original value; (b) reproductions, models or copies which, in certain conditions, may have the same value as the originals; (c) audio-visual and other aids to interpretation, which are becoming increasingly important.

    The conservation experts task is to preserve, with the help of physical chemistry, objects whose unique character and fragility call for a great variety of treatments. The greatest care must be taken with originals; the following remarks in this connexion should make it possible to pinpoint the problems. The archaeological museum, which calls for strict conservation measures, serves as a fitting model in this context.

    At the present time, faced as we are with a glut of information, original objects are the only sources of information which are constant and authentic and which cannot be tampered with. It is for just this reason that they never cease to afford new possibilities of interpretation. The original is the basis of the museum, its very raison dtre and the standard by which it is judged.

    The science and technology which are involved here in a great variety of ways make strict demands which can be clearly stated. It is not possible to deal with all the details in the context of this article. From the point of view of the architecture, however, one can, proceeding by simplification, reduce the fight against the ageing process, which in itself is ineluctable, to a common denom- inator: all conservation work is aimed at protecting the object against the depredations and the changing conditions of nature and placing it in a wholly or partly artificial, constant environment.

    In the same line of thought, the concept of conservation also extends to protection against damage and theft, since this has similar architectural implications.

    It is here that we come into seemingly insurmontable conflict with that trend in the social sciences which calls for the removal of all barriers and maximum contact with the exhibit, free access from outside and integration into the environment, free access to all objects inside the museum, open display (including the problem of maximum capacity) and hence a normal environment for the object and the visitor, and physical displacement of

  • , 206 Conservation

    objects so as to extend their sphere of influence, for example lending out for study purposes, etc. (Fig. 90).

    All of this is in complete contradiction with the requirements of conserva- tion which are based on the idea of there being a closed and constant environ- ment. The most advanced trends in sociology, in which openness is a key idea, and the demand of physical chemistry for a closed environment are diametri- cally opposed. It is therefore not surprising that the fundamental task of con- servation should be called into question and that the idea of a conservation- oriented museum clashes with that of a consumer-oriented museum. In this controversy, the stakes are high on both sides, but, in one case, the loss is irreparable. It is usually the exact sciences that win out, as they can offer a verifiable demonstration of their case, but this demonstration should not take the form of set formulae and simplifications, but of an intensive study of each particular case, In the field of social psychology, it is not possible to give such clear proof of destructions.

    Museum architecture must unquestionably meet both requirements as best it can, but placing the emphasis on one or the other, depending on the case. The social and psychological aspects should be considered in relation to con- servation and vice versa, this dialectical relationship determining the archi- tecture of the museum. Moreover, building entails an irrevocable decision. It is thus in the organization of space that the possibility of giving a new dimen- sion to these irreconcilable principles, and providing, where appropriate, a three-dimensional solution, is to be sought.

    Starting off with total conservation and going on to intermediate adjustable solutions, we shall present architectural models aimed at showing the different degrees of priority given to human or material considerations.

    In order to get as near as possible to an ideal state of conservation, the objects are kept in optimum technological conditions: Hermetic sealing-off from the outside world, with no inlets for heat, cold, etc. Temperature and humidity automatically maintained at a constant level by

    mechanical devices. Minimum access so as to avoid disturbances caused by the heat or humidity

    given off by the human body. Extended visits being scarcely possible, even for study purposes, special rooms with transition zones (air-locks) must be installed for the objects.

    Exclusion of most natural and artificial light. Artificial ventilation with filtered air, etc. When conservation is the chief concern, the architecture of the museum becomes an essentially scientific problem and the architect an assistant to the specialized engineer in its solution. Although a project of this nature does not call for any differentiation in the use of space, as it is all intended for the same purpose, the architectural implications, especially in relation to the environ- ment, may be considerable. The various possibilities are usually as follows: The storage building conceived as a closed and more of less independent unit

    is, on the one hand, very important from the point of view of town-planning, but, on the other, it is difficult to translate into formal terms and to express its function (comparison with the silo) (Fig. 91).

    Storage space surrounded by other premises, a solution satisfactory only for small museums; when there are large stocks, functional deficiencies appear in the surrounding sectors;

    Underground storage rooms, installed beneath the museum or outside it, cause, from the point of view of town planning, little disturbance to environ-

    9 1 Town skyline. A museum (or museum store-room) which is closed on all sides for conservation reasons, does not fit easily into the urban landscape.

  • Physiochemistrv of the obiects 207

    ments which may have some general value worth preserving. An inter- mediate solution consists in placing the storage premises in an accessible

    building with a roof-garden, a childrens playground, etc., which fits into the landscape (Fig. YZ(LZ), (b)).

    If the reserves are placed in a separate building, they can be moved further away at will (to the suburbs, for instance) since, in any case, transportation is necessary. Objects should be transported to the museum in air-condi- tioned, shock-proof containers.

    Since objects may require very different conditions for conservation, one thing that needs to be done is to create separate climatic zones which continue right into the display sections; this means that if the principles of conservation are to be systematically respected, climatology will be a dominant factor in the organization of the museum, which also has repercussions on the architecture.

    It must be granted that neither the idea of establishing an order of priority within the collection from the point of view of conservation nor the resulting architecture can be satisfactory and that, in most cases, such solutions have to be rejected on the grounds that they make the museum a mere machine for

    9 (a) Underground store-room with car parks, childrens play areas, etc., above. Simplified cross-section:.

    conservation. The machinery of the museum is far too complex to be geared only to this one function. It works properly only when all the cogs are meshing. Optimum conditions-especially in towns-can be obtained only by employing heavy technical plant at considerable expense. Such technical means are, however, burdensome, and for this reason it is to be recommended that, as far as possible, only natural means should be employed.

    In the developing countries, research is being carried out into the protection of museum collections by means of architectural climatology, that is to say

    92 (6) MUSEUM OF MODERN ART, Brussels. Underground museum in an historic quarter. Simplified cross-section. I. Entrance; 2. Reception; 3. Temporary exhibitions; 4. Patio; >. Collections; 6. Museum square; 7. Museum road; 8. New sections; 9. Car park. Architects: Roger Bastin and Leo Beeck; arch. ass. Pierre Lamby and Guy Van Oost.

  • 208 Conservation

    3 2 1

    4 9 --- A 4 6b

    I I-

    I-/ 93 Plan for the ideal museum with environmental control: buffered core for optimal environmental control. I. Core (maximum control); 2. Insulating corridor; 3 , Work areas, public areas; 4. Acclima- tization; 5 . Air-lock for main visitor traffic flow; 6. Minimal control: (a) Main foyer; (b) Shipping and receiving; 7. People; 8. Exhaust effect; 9. Works of art. Simplified ground-plan by Duncan Cameron (MzisezimNews, May 1968).

    94 Contact between visitor and exhibit: (a) direct contact; (b) the glass curtain effect.

    by applying the simple physical laws of construction so as to cut down the need to rely on technology. The simple method practised by Chinese museums, which consists in showing collections only when the seasonal macroclimate corresponds to the constant climate required by the exhibits, is not applicable everywhere. Figure 93 shows a museum in which the design emphasizes the conservation function.

    As has already been suggested, modern museum design for various reasons calls for transition zones (air-locks), the functions of which are: I. The physical acclimatization of objects when being moved from one cli-

    matic level to another. These spaces are situated mainly in the storage, administration and workshop sections and, from the architectural point of view, may be simply functional in design.

    2. The physiological acclimatization of the visitor to the varying climatic levels and to the relatively pronounced variations in lighting. The architectural solution calls for special study and know-how, since the transition must take place gradually by way of spaces which do not interrupt the tour of the exhibition but give a certain pattern to it.

    A distinction can thus be made between spaces serving to effect a transition between different degrees of lighting and between different climatic levels; these two kinds of intermediate space should not be the same. From the technical point of view, it is difficult to achieve marked differences of climate within the display section since the phenomenon of condensation, in particular, has to be reckoned with.

    Sections where the main concern is with display

    The capital constituted by the contents of the museum is of value to mankind only if it is in circulation, if it is productive. To achieve such productivity, architecture, must overcome the antithesis between conservation and display. The more extreme the two standpoints are, the more difficult is it to find the solution, but the more interesting and pleasing will be the result.

    Owing to the complexity of the problem, to which we have already drawn attention, it is necessary, in order to arrive at the right solution, to begin by studying the objects or groups of objects and determining their optimum physical parameters. The physical and chemical relationship of three sets of factors needs to be harmonized: the macro-climate, the micro-climate of the exhibits, the human micro-climate.

    Several combinations are possible depending on the degree of compatibility: I. The macro-climate cannot be regulated to the artificial conditions created for

    human beings and objects, which means that the outer shell of the building must protect the whole of the interior against heat and cold, damp, dust, etc.

    2. The micro-climates required for human beings and objects are not com- patible and the physical conditions in which the collection is shown affect the physiological well-being of the visitor or, conversely, the conditions created for his comfort affect the exhibits. This being the case, a climatic separation must be created between viewer and object which, for reasons of presentation, generally consists of a glass screen (Fig. 94(a), (b)).

    3. When there does not need to be any difference between the macro-climate and the internal climatic conditions, one can do without the external climatic shell and protect only the exhibits.

    4 . When there are only slight differences between the macro-climate and the display area, only the space in which the visitor moves within the museum may have to be provided with air-conditioning for reasons of comfort.

    T. When the three climates are almost identical (with material providing a fair degree of insulation-stone, for instance-in temperate zones), it is pos- sible to envisage a free layout which avoids many constraints and makes

  • Physiochemistry of the objects 7-09

    direct contact possible, although certain restrictions may need to be imposed for security reasons (Fig. 91).

    Each of these possible combinations calls for fundamentally different archi- tectural solutions, the separation of the different types of environment being a problem of architectural technique. Basically, there are two possible ways of organizing space: I. Separate rooms or groups of rooms with independent and diversified air-

    conditioning. The collection is exhibited in different sections with technical installations specially designed for the contents of each. The architecture must take this arrangement into account at the design stage. One problem that arises is the need to use the same sections of the building for more or less the same purpose and to keep the composition of the collections in them more or less constant.

    2 . The system of a space within a space, with air-conditioning for the object (mini-climate).

    In this connexion, a very free approach should be adopted to the use of show- cases. There are two basic ways in which they can be used.

    First, a set of showcases, freely positioned in space, with or without special air-conditioning, may be used. The showcases should be arranged in such a way as not to be directly exposed to the sun. Similarly, when artificial lighting is used, steps must be taken to prevent heat being given off inside (special filters for showcases) (Fig. 96).

    Secondly, continuous mural showcases, large sections of the exhibition area insulated by means of glass panels going right up to the ceiling and provided with separate air-conditioning, may be used. The showcases are usually built against the walls but may also be positioned in such a way as to be approach- able on all sides. Since they have a greater volume, the air circulates better inside them and it is easier to control the micro-climate (ceiling ducts, etc.)

    At a very early stage, a choice must be made between air-conditioned rooms and air-conditioned showcases, and between the set of showcases and the showcase-room. It should be clearly decided beforehand where the showcases are to be positioned in the rooms and whether they will be connected to the floor or to the ceiling.

    (Fig. 97).

    9J HAKONE OPEN AIR MUSEUM, Hakone. Open-air exhibition. Approximate harmony of conservation and presentation from the point of view of physical and physiological requirements.

    96 The 'room within a room' system for separate acclimatization of exhibits. Macro-, micro-, and mini-climates, separate air-conditioning ducts. Simplified cross-section.

    I \ I / - 0 - Macro-climate ,

    , , , , , . # . ,,;;,;;,;,::,::.~.~... 'I' ,',,'.I I...,. '..'

    I Micro-climate Mini-climate I o 1 tj I & I showcase n

    I 4 V I 4. I 4 V l t

  • 210 Conservation

    97 FEDERSEEMUSEUM, Bad Buchau. Site museum. The mural showcase extending up to the ceiling imitates the form of the window. (a) Interior view. The architectural space extends right to the back wall of the showcase. The panes, jutting in and out alternately, allow the objects to be seen from different angles. A combination of natural and artificial light provides the right intensity of illumination to prevent reflection. (b) Exterior view. Because of the very large windows one can observe the direct relationship between object and setting in which it was found: visual transition mini-micro-macro- climate. Architect: Manfred Lehmbruck.

  • Physiochemistry of the objects

    The creation of the greatest possible contact between the visitor and the object depends on the architectural solution adopted and on the technical characteristics of the dividing elements (transparent or opaque) (Figs. 9 8, 99).

    Dual - pu rpose sections The desire to balance conservation against display, considered to be both of equal importance, may produce a variety of answers to the organizational and constructional problems involved.

    P H A S I N G

    The objects are normally kept in store-rooms in which optimum conditions are provided and are shown in succession on a rotation basis for a relatively short time. Conditions of transportation are assumed to be optimum. It is not certain that this principle can be systematically applied, for the following reasons: I. Climatic conditions in the exhibition area must be the same as in the store-

    rooms, and its architecture, which should be adaptable, is thus .fixed once and for all.

    2. Even a very short time spent under different conditions may cause irrepar- able damage.

    3. In spite of every precaution, it is well-nigh impossible to avoid certain types of damage (in loading and unloading, from the jolts to which they are sub- ject on the way, abrupt changes in temperature, etc.).

    4. The museum can only with great difficulty open itself out, in the socio- logical and psychological sense: chances of conservation are no better for fragile objects (the only ones considered here), but the museum cannot properly fulfil its social function (Fig. 100).

    98 Large display cases forming movable dividing elements. Simplified cross-section. Air-conditioning of display cases (mini- climate) and of exhibition room (micro- climate) by means of ceiling ducts. Flexibility is possible.

    99 A circular showcase which can be viewed from all sides makes possible close contact between visitor and exhibit., Simplified ground-plan.

    Z O N I N G

    Since phasing in this way does not in itself provide a satisfactory solution, the spatial factor should be exploited to help to limit the dangers to objects and to achieve a compromise between conservation and display. This results in intermediate solutions in which now one aspect and now the other is stressed. These considerations lead to certain principles, one of which is the so-called filtering principle, which opens up to the visitor sections in which conserva- tion requirements are different. In the course of time, the collection may filter from one zone to another without any serious risks by passing through acclimatization rooms. It is thereby possible to obtain, if need be, several routes through the collection, the predominant feature varying between con- servation and display.

    In the sections which make less demands on display techniques, it is possible to accord more attention to the requirements of conservation. This could result, for instance, in three zones, with: (a) systematic storage of objects close together in darkened, entirely air-conditioned rooms; (b) less closely arranged storage in sets of shelves or in showcase-rooms with adjustable micro-climates, without too much attention to display; (c) widely-spaced display, designed for the public in accordance with aesthetic and sociological considerations.

    The size, the height, the lighting and the arrangement of the premises may be adapted each time to the required conditions. Nevertheless, great adaptabil- ity must be ensured within the sections so as to allow for changes of objects.

    It is possible, however, on the basis of the same principle to achieve not only filtering but also static zoning, which means that the collection is arranged more or less permanently in accordance with the considerations mentioned above. The advantage of this arrangement is that it makes it

    - ~ Store Museum

    100 Objects kept in store in optimum conditions are exhibited in rotation.

  • 212 Conservation

    IOI Diagram showing a balanced relationship between numbers of visitors and exhibits by means of spatial zoning of exhibition and conservation areas. This principle can be applied statically or on a phased basis.

    I ! ! i I ! !

    Many H O b j e c t s

    Few Persons

    Presentation Presentation Conservation I II

    possible to draw out the various qualities of the space and to harmonize them in the best way possible with the objects.

    These conservation-based models may be compared with public-oriented models which are concerned with the size and the quality of a given space. However, there is a conflict with conservation here in that it is just those objects which most deserve to be on show that have to be exhibited in the places least favourable to their conservation, although this objection carries a little less weight now there has been a change of attitude towards masterpieces considered as star attractions., The more art is seen in relation to its context, the broader and more even the basis of the interest in works of art-including those considered as secondary. The advantage of dividing the collection into zones lies rather in the field of organization and social service than in that of conservation. Most museums, if only for reasons of space, practise some such form of zoning.

    When the museum is being built, it is essential to analyse all the possibilities and their implications in depth (Fig. TOT).

    ,

    Lighting

    We shall examine below a few special matters which relate to the principles of conservation but which have a profound influence on architectural design. Strictly speaking, all light is harmful to the object and contributes to its ageing. The exceptions to this rule are only differences of degree, for example oil paintings, which do not need to be kept in total darkness. It is necessary to distinguish between: (a) damage resuIting from direct exposure to the action of rays and which may vary according to intensity, duration, wavelength (ultra-violet rays, for instance) and climatological conditions; (b) damage produced by the effects of lighting on the climate (for instance, raising the temperature of the rooms).

    Scientific measurements show the following values are to be acceptable and they are accordingly recommended: for organic materials, textiles, graphic works, maximum of 5 o lux; for oil paintings, maximum of I 5 o lux; for other objects, a higher or lower number of lux, according to the fragility, the thick- ness of the surface, the chemical composition, etc.

    The reflectance of the objects and the colour temperature must be taken into account. Ordinary daylight may exceed IOO,OOO Iux, which means that it nearly always has to be reduced in a museum. The type of lighting and the way in which it is installed are determined by the limit of tolerance of the object. This should be scientificallv calculated in each case. thus makine it Dossible to

    I 9. See also: Robert R. Feller, Control of the Deteriorating Effects of Light upon Museum Objects, MllseKm, Vol. XVII, No. z, 1964; and ICOM, La Lumikre et la Protection des obiets et SoCcimens

    arrange exhibits in groups according to their t~lerance.~ Generally speaking, it may be said that the deflation in the degree of con-

    ExposCs dans les Muses et Galleries dArt:

    Franaise de IEclairage, 1971.

    servation contrasts with the mounting inflation in the number of lux which is to be observed today.

    Eclairage dcr CEiurex dArt, Paris, Association

  • Physiochemistry of the objects

    Requirements thus differ not only within one and the same museum, but also between various types of museums. Thus, the original objects in an archaeological museum require quite different measures from those called for by the reproductions and models in a museum of technology. The architectural typology of the museum is strictly determined by the constructional measures which have to be taken for the conservation of the collection.

    Daylight varies greatly in intensity, direction, wavelength, etc., and is hence difficult to regulate depending as it does on the climate. The problem of day- light is inseparable from that of space and for this reason it is responsible for countless architectural successes and countless failures. Both static and mechan- ical means can be used to protect objects against the harmful effects and fluctuations of this light.

    Initial planning plays a decisive role. It goes without saying that an enclosed building with fixed and well-insulated walls, small apertures and a low level of lighting does away with many problems. But other, equally difficult prob- lems arise. Harmony between the space and the source of light is of prime importance. For instance, a very high room with a relatively small overhead opening may be well lit by the light reflected on to the walls; in addition, the height of the room facilitates the natural circulation of the air (Fig. 101).

    An opening facing the side away from the sun may have advantages. In the case of a saw-tooth roof or a similar structure, care must be taken that the architecture does not 'killy the exhibit. It may be necessary to have a ceiling through which the light is diffused, and this will have to be set fairly far away on account of the undulating contours of the shadow. Then, the intensity of the light will have to be checked to make sure it is adequate. In the case of a lateral wall built on the saw-tooth principle, its deliberately discontinuous character and the risk of dazzling and exposure to oblique light reduce the flexibility of the display. For reasons explained elsewhere, it is doubtful whether unilateral exposure, when a predominant feature, is a good thing (Fig. 103).

    I O 2

    I 02 High room with relatively small skylight. Good lighting due to: (a) the relatively high proportion of room area covered by the central light; (b) side light reflected from walls from a considerable height.

    103 Lateral wall built on the saw-tooth principle. Risk of dazzling and exposure to oblique light. Monotony, limited flexibility of display.

    There are various fixed appliances for the purpose of diffusing light and providing shadow. Absorbent panes of glass or film, the density of which can be chosen, go only some way towards reducing harmful radiation. In the case of objects which are sensitive from the aesthetic point of view (paintings), one must take into account the fact that they alter the colour of daylight. Absorbent panes which at the same time diffuse the light greatly are not suitable for objects whose effect lies in their form.

    Slatted or latticed sun-screens are effective only if they are placed outside the weather barrier (the pane of glass). Their shape depends firstly on the sun's orbit-in other words, on the latitude-and, secondly, on the direction

  • Conservation ' 214

    ro4 Claustra. The claustra casts a shadow on the exhibits and often (as is the case here this is not on the right scale, making the objects difficult to see.

    in which they are facing. If sun-screens are non-adjustable, it is difficult to eliminate the disturbing effects of light and shadow caused by the sun's chang- ing position, which can ruin a carefully planned display. The absence of main- tenance costs is an advantage (Fig. IO$).

    Adjustable regulating appliances are best suited to the variability of natural light, and afford the great advantage that the apertures can be kept open when luminosity is slight, and all the available light can be let in. They can be regulated according to the angle of incidence of the light, and they perform four functions: (a) they afford protection against the sun; (b) they regulate the intensity of the light; (c) they diffuse the light; (d) they may be used to reflect artificial light (inside). When fixed proportions are laid down, a single fitting cannot perform all these functions. The diffuser is not effective unless it is kept clean, which can only be done if it inside the building-but this is incom- patible with its being used as a sun-screen to regulate the intensity of the light. A dimming device is necessary, principally so that the effect of the light can be reduced as far as possible outside visiting hours. If there are only a few objects which need to be protected, it is possible to install a directed dimming device (for showcases, for instance). Automatic control is preferable, to ensure smooth running. It is often difficult to find room to install it, so it is as well to think about it fairly early on. Unfortunately, the visual disturbance resulting from the equipment available on the market affects the architecture consider- ably and also the intimate relationship between the object and the visitor, which is most important. The way in which such fittings are designed is of major importance for the museum using natural lighting. An unobtrusive and accurate regulating mechanism is still to be invented.

    Light coming from the side facing away from the sun (northern light or, for the southern hemisphere, southern light) has the advantage of being relatively constant with regard to both its physical quality and its physiological eEect. A certain monotony is inevitable when it is used exclusively, especially when the light is not very intense. This reduces the validity of one of the main arguments in favour of daylight, namely that it is subject to variations, which are the essence of life. One can perhaps go so far as to say that a choice must be made between a complicated device to provide protection against the sun and an excessively bleak monotony. Differences in the quality of the light open up possibilities in the interpretation of the objects. In practice, when light from the north has been chosen for reasons of preservation, it has proved profitable to enhance it by means of a certain amount of southern light, possibly in the

    '

  • Physiochemistry of the objects 2 I J

    form of reflected light. Lighting from one side throughout an entire building has a leaden effect on the basic architectural design, and makes it necessary to arrange the various rooms on the same lines. It is possible to introduce a greater or lesser degree of variation between rooms, but the fact that the light always falls on one of the sides and that the other side is invariably chosen as the hanging surface is psychologically inhibiting and produces stereotyped patterns of presentation.

    Reflected light has a greater effect and significance than is generally recog- nized, owing to the fact that daylight, which in any case is diffuse, rebounds off all the surfaces in the room. The reflectivity, the colour and the structure of the surfaces give the whole room its tonality. In general-particularly in hot countries-the lighting and heating effect will be still found to be pronounced. One of the advantages of indirect light lies in the fact that the harmful ultra- violet rays are absorbed in the course of the phenomenon of reflection; its disadvantage is that it alters the colours in a way which is not desirable in a museum. In the architectural conception of the problem of lighting, indirect light should be usd for background lighting and direct light to add emphases.

    Reflections from surrounding buildings and trees can be very important, and may become a decisive criterion in the choice of a site. For instance, many of the opportunities of using daylight are lost if there is a skyscraper towering up in front of the sun (Figs. IOJ, 106).

    Humidity and temperature

    Temperature and humidity are closely bound up with the problem of light. The reader will get some idea of what this means from the fact that, in a building in which 50 per cent of the surface area of the outer walls consists of glass panes, the latter are responsible for as much as 80 per cent of heat-loss. Here too, constancy is desirable. Fluctuations over a long period are less harmful than sudden variations in temperature, as is shown by the relatively satisfactory state of historic works of art that are kept in buildings in which the temperature varies little (churches, for instance). Recommended temperatures range from about 1 8 ~ to zoC for an atmospheric humidity of JO to 66 per cent, with a maximum of 70 per cent in damp climates and a corresponding temperature. It is to be noted that even these figures constitute a compromise with the conditions of human physiology, since considerably lower tempera- tures are better for the preservation of more fragile objects. The measures to be taken depend, on the one hand, on the geographical and urban situation (dust, fumes, etc.) and, on the other, on the physiochemical make-up of the object. If the temperature-humidity ratio is higher or lower than the appro- priate figure, either dehydration, cracks, etc., or condensation, accompanied by the formation of mould and bacteria, will result.

    With regard to planning, it is to be borne in mind that it is basically easier to humidify than to dehumidify. While it is possible, to a certain extent, to achieve humidification by natural means (by providing water surfaces), dehumidification can be performed only by mechanical means. At the stage of architectural design, care should be taken to avoid the formation of stagnant air-pockets which could give rise to mildew. This makes it necessary for studies of fluid dynamics to be carried out, with a view not only to allotting the space available but also to arranging the rooms. Fumes can be eliminated only by ventilators provided with filters, which may be used for general air-con- ditioning or be specially designed for certain objects (for instance, an air-filter which absorbs sulphur dioxide).

    According to the nature of the exhibits, steps must be taken to ensure that the whole of the museum is dust-proof, which means either installing an artificial ventilation system or placing the exhibits in dust-proof showcases, with or without ventilators. In manv countries-esDeciallv in troDical areas-it

    2h

    rol Roughly speaking, daylight can be considered adequate when the ratio of the height of a neighbouring building to its distance from the window is at least I : 2. Simplified cross-section.

    -0-

    106 The tendency of a reflecting wall to affect colour and raise temperature (particularly in warm climates).

  • 216 Conservation

    IO. See Appendix II, page 269.

    is recommended that visitors be made to pass through an unobtrusive device which absorbs dust and humidity.

    N A T U R A L V E N T I L A T I O N A N D D A Y L I G H T

    In museum architecture, the requirements of conservation can be met at very different technical levels.

    If natural ventilation and daylight are chosen (artificial lighting being used merely to supplement it), efforts will have to be made to meet the main require- ments by climate-adapted building, that is to say by using only specifically building techniques to regulate the effects of the climate.10 These may be: I. In the general planning of the project and the over-all design of outer walls

    comprising a proportion of openings and of enclosed areas adapted to the contents of the collection, providing for the openings to be facing in an appropriate direction and, if need be, for an arrangement which is in accord- ance with the principles of fluid dynamics. It is also necessary to take account of environmental engineering from the ecological point of view, especially with regard to the humidity rate and the reflection of heat.

    2 . Determining the dimensions of the rooms on the basis of the climate, for instance: rooms with high ceilings in a hot climate, natural circulation of the air both vertically and horizontally, etc.

    3. Providing for weather-insulation and employing appropriate building techniques (walls of several thicknesses, double glass panes, etc.).

    4. Using materials capable of withstanding extreme climatic conditions, for instance: hygroscopic materials in a dry climate, waterproof materials in a damp climate, etc.

    Such measures-which cannot all be dealt with here-have a profound influ- ence on museum architecture, but they must be adapted to each particular case. They afford the advantage of not giving rise to mechanical breakdowns and not entailing large operating costs. If they are to operate economically, however, a higher outlay on the building is necessary. Owing to considerations relating to natural ventilation (high ceilings, air-cushion, etc.), the volume to be built will be greater than other factors would necessitate (Pig. 107).

    Although climate-adapted building makes it possible to obtain appreciable results, its possibilities are limited. If one relies on its effectiveness alone, un- satisfactory conditions of conservation will often have to be accepted.

    A R T I F I C I A L A I R - C O N D I T I O N I N G A N D D A Y L I G H T

    For this reason, most museums employ artificial atmosphere regulation, while continuing to use daylight. Atmosphere regulation-or air-condition- ing-may be partial or complete. In general, one starts from the principle that the most important rules associated with climate-adapted buildings should be obeyed, and that a mechanical air-conditioning plant should also be provided. As one will certainly wish to take advantage of the excellence of daylight for displaying the exhibits, the air-conditioning plant must perform the following functions: (a) make it possible to obtain maximum benefit from the daylight and to guard against its fluctuations; (b) offset sudden changes in the weather that the building material (glass, for instance) cannot absorb; (c) in most cases, overcome the effects of heat or cold; (d) keep fresh air circulating. In comparing the cost of complete mechanical air-conditioning with that of a solution based solely on climate-adapted building, it should not be forgotten that the first may require as much as a third of the total volume of the building, depending

  • Physiochemistry of the objects 217

    f f 1111111 ,-A L,ll 1111 II

    on the size of the unit, and that, generally speaking, it does not lead to a reduction in the volume built. From the technical point of view, it is recom- mended that the building be divided up into sections according to the different types of environment and use (conditioning of the object, special sections). In a museum lit by daylight, it is often difficult to house such bulky machinery. For the sake of the psychological economy of the display section, the exhibits should not have to compete with radiators, exhaust pipes and ventilation shafts; in other words, the latter should be in the background or not visible (concealed, for instance, behind false ceilings or walls). From the stage of architectural planning onwards, allowance must be made for the large amount of space required by the air-conditioning conduits, and this may in some cases have a decisive effect on the project (Fig. 108).

    107 Diagrammatic suggestion for acclimatization in a hot, dry tropical climate. Simplified cross-section. Movement of air through and up a central hall which acts as a chimney, extending vertically the height of the building. Humidity ensured by air sucked in over water surfaces. Shade from roof projections perforated for ventilation. (Design varying according to direction in which the museum is facing.)

    A R T I F I C I A L A I R - C O N D I T I O N I N G A N D A R T I F I C I A L L I G H T I N G

    Technological progress in the creation of an artificial environment has finally reached a stage at which both lighting and atmosphere regulation are entirely artificial. This poses problems which belong to the technical sphere. Constancy, flexibility and regularity can undoubtedly be guaranteed within fixed limits. The outer walls can be closed and can be well insulated; large installations and pipe-systems can be positioned and controlled visually. Even where there are undesirable light-rays, they can be investigated and dealt with more accurately than can daylight; an artificially regulated atmosphere can be kept constant.

    The focal point of the architecture becomes the arrangement of internal space, on which the relationship between the object and the surroundings depends. The problem of light is really a question of the technique used for lighting. If all the opportunities offered by artificial lighting are used, a large,

    I l I I I l I I- I = I_ I I _ L r

    Pressure gradient

    108 The pressure gradi.ent of air-conditioning systems designed to meet conservation requirements should lead down from sensitive towards less sensitive areas or exhibits. The arrangement of the rooms should be taken into consideration at the earliest possible stage in planning. Simplified ground-plan.

  • Conservation

    109 Plan for a multistorey museum lit by daylight. Simplified cross-section. Light should preferably be obtained from north-facing windows or skylights (south- facing in the southern hemisphere) in order to avoid exposing the exhibits to direct sunlight. Satisfactory lighting of the lower storey is difficult.

    II0 In multistorey buildings higher storeys may be set back to allow daylight to enter through the roof of the storey immediately below. Oblique light, illumination decreasing sharply from top to bottom of the wall, relative darkness of the middle of the room. Simplified cross- section.

    I !

    4 h d

    III Museum lit exclusively by artificial light: extensible on a vertical plane (cumulative); extensible on a horizontal plane; flexibility of presentation; adaptable lighting (the direction, intensity and nature of the light may be changed at will). Conservation is considered the first priority.

    II. See page 205.

    flexible space (open plan design) must be chosen. Consequently, there will be no appreciable distinction between this space and other neutral structures which are used for all kinds of purposes and which are to be found throughout the world.

    The differences are so deep-seated that a basic distinction must be made between a museum using daylight and a museum using artificial light.

    A museum using daylight, establishing as it does a dialectical relationship between man, space, light and object, is complicated and makes no claim to perfection in the rational sense. Primary importance is accorded to man and display, in their sociological, psychological and physiological interdependence. There are many obstacles to the free development of this relationship, but they call forth unexpected solutions. Two building problems predominate: first, the number of storeys. If a museum using daylight is to be used effectively and afford the same resources as a museum using artificial light, it must be able to avail itself of the whole spherical horizon. Only a single-storey museum can fully meet this condition; if similar conditions are to be obtained in a building of several storeys, the different storeys must each be set back considerably.

    It is not satisfactory to set them back a short distance, on account of the oblique light and the reflection of the wall above.

    There remains the problem of the middle area, which, in certain cases, is not sufficiently well lit by daylight to meet the requirements of display (Figs. 109, I I O ) .

    Secondly, flexibility is much reduced. A museum using artificial light places most emphasis on the preservation of

    the exhibit, for the sake of which the visitor and most of the exhibits have to exchange their natural environment for the artificial environment of the museum. For this purpose the architecture offers the setting of a large, super- imposable and highly adaptable space. The space within which the specific museum experience takes place is arranged after the basic setting has been established, like a theatrical setting. In the absence of overriding considerations, the architecture can provide only a neutral structure resembling that of ware- house. As to its fitting into the urban framework, there are two possibilities, which are mentioned at the beginning of this chapter.ll

    A building which goes back a long way, which has glass walls, and is mainly lit by artificial lighting, is in much the same position as an artificially lit museum (Fig. I I I ) .

  • Physiochemistry of the objects 219

    II2 DENVER ART MUSEUM, Denver. Artificial light only is used for presenta of the exhibits. The scattered window I serve the purely psychological purpose providing orientation and a change of scene. Architects: James Sudler Associates, Denver; Gio Ponti, Studio P.F.R., Milan.

    tion ;lits of

    Since ecological and sociopsychological considerations are also involved, an interdisciplinary problem arises. The choice between daylight and artificial light should be made in each individual case bearing in mind considerations relevant to the human and the exact sciences. In one case, the architecture is also a clear expression of what occurs in the museum; in the other case-if it is to be consistent-its effect is neutral; the implications of the decision are such that economic considerations should not be decisive (Fig. 112).

  • 2 20

    Side entrance

    Hospitality

    Creative activities

    I I i I , I

    Temporary exhibitio

    Main entrance

    D .....

    O Public Internal I I

    Semi-internal I Semi-public

    II? Schematic path diagram. The main lines of communication between different sections and areas, indicating varying degrees of accessibility to the public.

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