Conservation Physics - Index
Conservation of paintings in thermally unstable environments (September 2019)
A study of the effect of back protection on the RH behind paintings on canvas which are exposed to a varying wall temperature.
Introduction to this compendium of articles on preventive conservation and building physics applied to historic materials and structures.
A light hearted introduction to preventive conservation
An introduction to concepts and units concerning heat, moisture and light, which affect the interior environment.
A calculator for deriving moisture concentrations in air from dew point and psychrometer data
Vapour pressure of water in air, explained through the swelling of a tea bag.
Definitions and explanations of the usefulness of mixing ratio and absolute humidity
A calculator for deriving the temperature at which a certain RH is attained
Calculate the energy needed for dehumidification of storage spaces, given the interior temperature and target RH.
A calculator for estimating the energy consumption associated with the climate specification and the design of a building.
The effect of light on museum objects with particular attention to colours
An explanation of the fundamental SI unit for light intensity, from which all other luminous units can be derived.
Information on the light-fastness of natural dyes is reviewed. New tests on the fastness of several dyes in fluorescent lamp light are reported.
This is a review of research on the deterioration of cellulose through exposure to light, ultraviolet and high energy radiation. The literature coverage stops at 1969, but the radiation sensitivity of cellulose was by then adequately researched because of the widespread use of cellulosic fabrics in aircraft construction before 1930.
The lux gives great weight to light at about 550 nm, which is far from the most damaging radiation at about 400nm
The sorption isotherm describes the reversible absorption of water by materials exposed to a changing relative humidity
The exchange of moisture between materials and air
The sorption of water by wood and its effects on the physical dimensions of wood.
Permanent set in wood caused by unsymmetrical moisture stress
Water vapour transmission through a porous material in a temperature gradient seems to depend on the water vapour concentration gradient rather than on the vapour pressure gradient, as is often assumed.
A description of the concepts of stress and strain with particular application to paintings on canvas.
A story which illustrates the efflorescence of inorganic salts as the relative humidity fluctuates
Proceedings of the conference 'Museum Microclimates' held in Copenhagen in 2007
There is a large risk of condensation when cooling or warming happens quickly. The thermal inertia of materials generates large temperature differences over small distances which can cause acute condensation.
A tutorial on packing an object for transport, with a paper wrap, then polyethylene, then insulation.
A story about the effect of changing air pressure on the relative humidity around goods in transit
On the difference between heat flow into an enclosure and the temperature which it reaches
A Himalayan legend describes the surprising consequences of moisture movement caused by temperature gradients in small enclosures.
A glimpse into the microclimatic mysteries of glass cases.
The climate in a glazed picture frame is surprisingly violently affected by exposure on an outer wall or to direct sunlight indoors.
The climate behind the oil paintings mounted on the outer walls of the Baroque chapel of Ledreborg house in Denmark is surprisingly benign, compared with the climate in the chapel.
A woven silk picture transferred its image to the glass against which it had been pressed for fourteen years. The image was formed from salt, which occupied the areas where the silk had not touched the glass. Salt impregnation increases the water absorption of silk at a relative humidity below the value at which pure salt deliquesces. A salt solution had formed in the fabric at a moderate relative humidity and then migrated to the glass where the salt precipitated because the relative humidity was below the deliquescence point of pure salt. The process has been replicated.
An experiment with a picture set against a variable temperature 'wall' and protected by back plates with varying hygroscopicity and placing.
The working principles of a humidity chamber for moistening art without risking condensation
A tutorial about the measurement and interpretation of the air exchange rate and introduction to the calculation of moisture buffer capacity in enclosures.
The effect of absorbent materials and restricted air exchange on the course of the RH in showcases and picture frames.
The influence on the room climate of moisture absorbent insulation in the exterior walls of houses
As air pollution in cities diminishes, or at least changes its nature, the air pollution generated within buildings becomes a relatively more serious cause of deterioration. The low rainfall indoors allows hygroscopic salts to develop and remain, without ever being washed away. Nearly airtight enclosure brings the threat of damage by modern materials outgassing into the air around museum objects, as well as chemicals given off by self-destructive objects. The commonest indoor pollutants are acid gases from the decomposition of wood, cellulose acetate and cellulose nitrate. Acid attack requires a thin watery film on the surface of the object to allow ionic processes to occur. Within showcases, there is competition between absorption on the object, absorption on a sacrificial absorber and ventilation out through imperfections in the seal.
A lecture to the lime forum in 2011 about the concept of breathability applied to buildings
Heat and ventilation are both necessary to drying. An experiment shows the relative importance of these two influences and how to dry without over drying to equilibrium with a low relative humidity
The persistent emphasis on the need for ventilation to suppress mould growth is wrong and forces unnecessary complexity and cost on environmental control.
A cool plate for conservation studio use, as well as research. A temperature range of 10 ° to 40 ° C can be programmed and also remote controlled.
A cold store for small collections of film which works by slightly warming a box within an ordinary food freezer.
The interaction of water vapour with paper, with particular reference to humidity buffering of leaky spaces where the kinetics of water movement through paper is significant.
The player's breath causes condensation within the joints of woodwind instruments causing the joint to swell against the outer band of wood, metal or ivory. On drying, the joint contracts to a smaller diameter, throwing the instrument out of tune.
Climate measurements show the performance of sealed versus open grave chambers and the advantage of an impermeable floor covering
A cooled case using thermoelectric cooling
The principles of mechanical air conditioning in large buildings
An explanation of the construction principles of the Mollier diagram and its almost identical alternative - the psychrometric chart.
A comprehensive account of the physics of the microclimate in stores without explicit temperature control
Allowing a moderate annual temperature cycle in a museum store allows a much simplified and energy efficient control of RH.
A review of the moisture buffering performance of construction materials and an introduction to the B-value concept for estimating the moisture buffering by artefacts.
The idea that a massive building gives a good archive climate is not as clear cut as one might think.
Material for a course in the design of museum storage: lectures, articles and exercises.
A phd thesis on moisture buffering by construction materials. Chapters on the fundamentals of the interchange of moisture between air and materials
Examples of museum buildings which have suffered condensation in the structure caused by leakage of humidified indoor air through the outer walls and roof.
Drifting temperature with dehumidification provides a cool storage environment, but will environmental standards allow this?
Semi passive relative humidity control by mixing heat flow from the outside and heat from the building interior
How to use absorbent materials in walls to buffer the relative humidity in archives and stores.
A suitable choice of building materials would give museums a stable climate without air conditioning.
A review of trends in modern museum architecture which reduce the natural stability of the indoor climate but paradoxically increase the possibility for stabilising it without massive air conditioning installations.
The air conditioning needed for film archives, analysed in relation to Arrhenius plots of the rate of deterioration.
Low energy storage - article in ICOM-CC 2011
A review of the influence of building construction techniques and materials on the inner climate, with a section on biological growth in houses.
Humidity buffering by porous walls has a considerable moderating influence on the indoor climate.
Museum environment standards inhibit the use of simple climate control, particularly in storage, through their insistence on fixed temperature limits and expensive storage protocols.
An examination of five control strategies for controlling the temperature and relative humidity in stores containing an abundance of moisture absorbent materials.
Illustrations of the interaction of the local climate with a building without mechanical air conditioning.
Museum stores which use the earth below as a temperature buffer hold a moderate temperature all through the year. Dehumidification is necessary in summer. It can be solar powered.
A lecture about low energy museum design, delivered to the AIC meeting, Philadelphia 2011
An analysis of the north European climate and of the preservation requirements of typical museum objects suggests a suitable low energy method of air conditioning a museum store designed to hold relatively durable materials: outside air is sucked in when its water vapour content is unusually low while the temperature is raised slightly to give a relative humidity not far below the limit for biological growth. This combination gives a low degradation rate for both objects and the building that encloses them.
Solar heating plus temperature buffering by ground and humidity buffering by construction materials provide fully passive climate control for a museum store (pdf)
The theory and practice of using saturated salt solutions to define a relative humidity for sensor calibration or for treatment.
Measuring stress and strain in the context of conservation and building physics.
The thermocouple: how it works and how to use it.
Data loggers for climate measurements, with hints on how to choose and use sensors.
A description of a climate chamber designed to measure the moisture absorption and release by materials and constructions exposed to a changing moisture flux.
An instrument is described which allows the eye to detect sources of ultraviolet radiation. Coincident ultraviolet and visible images of the scene are viewed through an eyepiece. The suspected source of radiation is centered in the field of view. The visible image is then extinguished by operating a shutter. Ultraviolet radiation is revealed by yellow-green fluorescence from a small target in the centre of the field.
How to use a camera as a lux meter, particularly for estimating lux within an inaccessible showcase.
How to use awk and other unix utility programs to convert and merge climate data files ready for plotting with gnuplot
An explanation of the science behind the Image Permanence Institute's Preservation Index and Time Weighted Preservation Index
A criticism of the environmental advice in British Standard 5454-2000 for archives.
The present museum standards for temperature all demand constancy to a degree or two. There is no evidence that this is necessary. It is surely just the assertion of what is thought possible with air conditioning. This article is in 'Going Green', British Museum, April 2009
Several articles and publications challenging the strictness of temperature standards for museums and archives and proposing a more open development process.
A simple and direct and un-pompous proposal for a museum environmental standard.
The 1996 exhibition made for the IIC congress in Copenhagen "Archaeological conservation and its consequences"
A review of the Bologna Symposium on Science, Technology and European cultural heritage, 1989
A book review in Studies in Conservation, 1965
List of publications by Tim Padfield
Sustainable climate management strategies. A workshop organised by the Getty Conservation Institute on Tenerife in April 2007
Passive design,mechanical systems and doing nothing: a telephone discussion about environmental management. in the Getty Conservation Institute newsletter 22.1, Spring 2007
All articles in this Conservation Physics compendium, except the external links, are licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.