Atoms form molecules by means of their electrons. Electrons move very fast through the atoms in a way which makes it impossible to determine where an electron is located at a given time. There is only a statistical certainty that electrons are in a given zone around the nucleus of the atom. Which zone this is depends on the amount of energy that an atom has at a certain moment in time.

The different zones in an atom could be somewhat compared to an onion, whereby every layer could be a limited zone where electrons can be found. These layers are called “shells”. In the inner shell, closest to the nucleus of the atom there is only space available for 2 electrons. For H (hydrogen) with 1 electron and He (helium) with two electrons this is no problem. There is enough space available. But for Li (lithium) with 3 electrons another solution is necessary. So the third electron moves to the following shell which is situated more outwards from the nucleus. This 2nd shell can contain 8 electrons, just as the 3rd shell. The 4th and the 5th shell can contain up to 18 electrons, the 6th shell up to 32 electrons.

Lithium - Pumbaa

Photo: Lithium atom - author: Pumbaa

Every time a shell has been filled the other electrons are moving up to the next shell. Chlorine with 17 electrons has 2 electrons in the 1st shell, 8 in the 2nd shell and 7 in the 3rd shell. The more shells there are, the larger the atom. We can see this by comparing the diameters of C (6 electrons) and gold (79 electrons). The diameter of C is only about half the size of the diameter of gold.

Atoms continuously strive to reach full electron shells. They do this by taking up, giving off or sharing electrons with other atoms. It is a mechanism depending on chemical reactions and leading to the formation of molecules.

Covalent bonds

Let us look at the molecule “methane”. Methane consists of 1 carbon atom (C) and 4 hydrogen atoms (H). Carbon has 6 electrons, of which 2 are on the inner shell and 4 free electrons on its outer shell (2nd shell with ultimately 8 electrons). Carbon is 4 electrons short of a full outer shell. Hydrogen lacks one electron in its outer shell (1st shell with maximum 2 electrons). The carbon atom needs to combine with 4 hydrogen atoms to fill up its outer shell (4 + 4x1 electrons). Hydrogen only needs 1 electron to complete its outer shell. So the carbon atom unites with 4 hydrogen atoms, forming 4 electron pairs (4 x 2), resulting in full outer shells for all atoms. By doing this methane becomes a stable molecule.


Photo: Methane molecule - author not found

This kind of binding is called a “covalent bond”. The electrons are shared, on an equal basis, between the carbon atom and the 4 hydrogen atoms. That way each atom has, notwithstanding the motions of the electrons, always a full outer shell. The molecule has no extra free spaces anymore and therefore is in equilibrium. It has no need anymore to form new relations. It forms therefore a stable unit. Only when heavy collisions would occur or when enough external energy would be added, bonds could be broken.

The result is a chemical reaction. This is what happens when we burn methane as natural gas for cooking or heating. Methane molecules have no common interest in each other. They live in a loose connection that we call a “gaseous form”.

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Photo:Combustion of methane - author: Essent Energy

When we look at a water molecule we see a different story. Water exists of 1 oxygen atom with 8 electrons, (of which 2 are in the inner shell and 6 in the outer shell) and 2 hydrogen atoms (each with 1 electron on the outer shell). Oxygen needs 2 electrons to complete its outer shell. But oxygen is quite dominant and does not share the electrons on an equal basis. The oxygen atom sits between the two hydrogen atoms and in fact attracts the hydrogen electrons towards the center with as result that these electrons are closer to the oxygen nucleus than they would be in methane.

The result is that the hydrogen atom, because it partly looses a negative ion, receives a small positive charge. The opposite is true for oxygen. Because this atom attracts 2 negative electrons, it gets a more negative charge. We know that equal charges reject each other and that opposite charges attract each other. Because there are two slightly positive atoms in water these move slightly away from each other. You can see this in the drawing below. We call this effect “polarity” and we call this kind of molecule “polar”. Polarity has an effect on the properties of the molecule.

Dan Craggs-water  pl-olarity1.svg

Photo: Polarity of water - author: Dan Craggs

The reason why water molecules attract each other is due to the fact that the negative oxygen atom of one molecule attracts the positive hydrogen atoms of another water molecule. This way mutual connections are formed which we call “hydrogen bonds”. These bonds are partly responsible for the inner structure of cellulose and responsible for binding water in, for example, paper.


Photo: hydrogen bonds - author: Qwerter

Covalent bonds are mostly fairly weak bonds. Most molecules with covalent bonds have a liquid or gaseous form. The compounds they form mostly have relatively low melt- and cooking points.

Guy De Witte

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To gain a better knowledge of the properties of objects and the dangers they are exposed to, it is important to have a better insight in their composition and the processes that have a negative impact on them.

This insight demands a basic knowledge of chemistry, physics and biology. Because not everybody involved in art and cultural heritage has this knowledge (maybe because it was never learned or maybe partly forgotten) we want to provide this basic knowledge through our blog/site. Sometimes we use a more simplified way for a better understanding.

Today we start with “THE ATOM”.

What is an atom?

The word “atom” is derived from the Greek word “atomos” which means ‘indivisible”. The ancient Greeks thought the atom was the smallest particle in the universe and that it was indevisible. Today this idea is outdated.

But the atom remains the smallest building block of which all matter and materials, as well vegetable as animal or mineral are composed of. Atoms are the “lego blocks” of nature. There are different kinds of atoms. They have a different composition and different properties and can be combined to form living materials or non-living materials. The way they combine happens according to coded instructions inherent to nature. These instructions can be of a physical or chemical nature. They are a kind of “manuals” according to which the building blocks are combined to form an entity. Because these “manuals” are often more “guidelines” instead of a strict program, it is possible to find a lot of variations on the theme, especially in living materials. Living creatures or objects composed from once living matter we call “organic”. Non-living materials we call “inorganic” (= non-organic).

How is an atom structured?

Atoms have a diameter of about one tenth of a million of one millimeter. This is very small and invisible for the naked eye even using a normal laboratory microscope.

An atom consists of smaller particles of which we will only mention the ones most important to our purpose: protons, neutrons and electrons. The most simple representation of an atom is comparable to our solar system: a central core (consisting of protons and neutrons) around which circulate smaller objects (electrons). In practice the system is more complicated. The electrons move at a crazy speed aorund the core and not in planetary orbit as our planets, but criss-cross through a spherical or elliptical space around the atom core.


Representation of atom (Adrien Facélina)

The amount of protons can be equal or not to the amount of neutrons. In an atom there are always as many protons as electrons. Protons have a positive electrical charge, electrons a negative electrical charge. This way the particles keep each other balanced. Neutrons do not have electrical charges.

The core of an atom is very small. The diameter is about 1/1000 of the total diameter of the atom. The electrons are smaller still. Everything in between is empty space, which allows for a lot of movement. All objects, even living creatures are thus composed of a lot of empty space.

There is a whole variation of atoms. This is based, amongst others, on the different amount of protons and neutrons in the core. The properties of these atoms are therefore different. Atoms can contain up to 92 protons. Based on the amount of protons the atoms have received what we call an “atom number”. All these atoms occur in nature. Number 92 is uranium. Every type of atom has specific properties and behaviour and react in specific ways with other atoms. There are also atoms with a higher atom number (up to 118 nowadays), but these atoms are not occurring spontaneously in nature. They can only be synthesized with scientific equipment.

The table of Mendelejev

Based on the diversity of properties the Russian Dmitri Mendelejev devised a clear table of elements for all known atoms in his time. Elements have been added to this table when they became available. This table shows the various relations between the different atoms.


Table of Mendelejev (DePiep)

Names and symbols

Each atom is represented by a letter symbol. Mostly, but not always these are the first letter(s) of the Greek or Latin name for the atom. So the letter H stands for Hydrogenium (Hydrogen), He for Helium (Helium) and Cl for Chloros (Chlorine).

In conservation practice we will encounter often the same atoms. That is why it is important to know the exact names, shortenings and properties of these atoms. Lacking the right knowledge can have a large impact on conservation and survival of materials.

The most occurring atoms we will work with are: H (hydrogen), C (carbon), N (nitrogen), O (oxygen), P (phosphor), S (sulfur), Cl (chlorine). Depending on the materials we work with we will also need knowledge of Na (sodium), Mg (magnesium), Al (aluminium), Si (silicium), K (potassium), Ca (calcium), Fe (iron), Ni (nickel), Cu (copper), Zn (zinc), Ag (silver), Sn (tin), Au (gold) and Pb (lead).

In a next post we will cover the interaction between identical and non-identical atoms.

Guy De Witte

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People who are acquainted with me will know that climate change and its possible impact on life on earth has always been a topic I have been interested in. My first confrontation with climate change dates from 1972 when the Club of Rome published their report “The Limits to Growth”. At that time is was already clear that Humanity lived above its means and that sustainability would become a hot topic in the future.

Through the years sustainability has become more and more important, also due to the actual climate change, of which we gradually start to see and feel the consequences.

Since I am professionally involved in conservation of cultural heritage it was a logical step for me to get more and more involved in analyzing data and extrapolating possible repercussions on art and cultural heritage.

That is why I chose, in 2006 : “Archives in a Changing World: An Exploration into Sustainable Building for Archives in Belgium in Response to Global Climate Change.” as title for my thesis to acquire my Master in Preventive Conservation at Northumbria University in Newcastle (UK).

The result was an invitation by the organisers of the “Going green” conference in the British Museum (Clore Education Centre) in 2009 to present a paper named: “New Challenges demand new solutions: The Integration of Sustainable Building and Functioning of Archives as a possible response to Climate Change.”.

The same year I produced an article for the magazine Faro (published by Faro, a leading cultural heritage organisation of the Flemish government), with the title: ”Klimaatverandering en duurzaamheid. Sleutelwoorden voor een nieuw erfgoedbeleid (”Climate Change and Sustainability: Keywords for a New Cultural Heritage Policy”).

Since then I try to get climate change more and more on the cultural agenda by giving talks about the threats posed to our cultural heritage. One of the examples is the serie of talks called “Buitenbeentjes” (Mavericks) in 2012 where I asked the question: “Can the World save its Heritage”.

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Foto: Guy De Witte: "Can the World save its Heritage?"

The last paper was at the conference “Art meets Security 2015”, where I talked about: “Climate Change: a Global Threat to Art and Cultural Heritage”.

My students of the courses in Cultural Heritage Education, Archive Education and Master in Cultural Heritage and Temporary Document Management are every year again made aware of this growing problem.

Even so I notice that in Belgium and some other countries the awareness of the impact of climate change on our cultural heritage is still minimal and that although large international organizations are discussing how to tackle the problems, most institutions are only focused on local institutional issues. That way they miss the big picture and decisions taken on a local level for improving conservation conditions may be contraproductive in the long haul. This is a pity since the problem begins to be urgent and future policies will have to take climate change more seriously. This will be the only way to mitigate and manage the oncoming problems.

Climate change will as well have a large macroscopic as a microscopic impact on the survival of cultural heritage. Macroscopically whole sites are threatened such as the natural sites of the Great Barrier Reef in Australia and the Kilimanjaro National Park in Tanzania. But also known archaeological sites as Chan Chan and the Machu Picchu complex in Peru are very vulnerable.

However the threat does not limit itself to these sites. Hundreds of cities all over the world are threatened. Two thirds of all cities with more than 5 million people are situated less than 100 km from the coast. Nearly 650 million people leave on land that is less than 10 meter above sea level. In Europe Denmark, part of the coast of England, Belgium and especially The Netherlands are in the danger zone. It is also in all those cities, close by the sea, that we find the largest concentration of art and cultural heritage. It is a quantified certainty that cultural heritage is now threatened worldwide.

International organizations such as UNESCO, ICOMOS and ICCROM sounded the alarm-bell already years ago. UNESCO published in 2007 a publication called: “Case Studies on Climate Change and World Heritage”. In this publication cities as London, Venice, the heart of Prague and Timbuktu (Mali) are considered as threatened. In London it concerns the complete site of Westminster, the National Greenwich Museum and the Tower. Venice is completely threatened, not only because the sea level rises but also because the city is sinking into the lagoon.

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Foto: Unesco Publication

For The Netherlands the situation will become dramatic over time. One third of the country lies below sea level and the water level of its main rivers. It is protected by dunes, dikes and the Delta Works flood barrier, an ingenious flood barrier system. Even so, nobody can guarantee that climate change cannot alter this situation. If massive flooding occurs there will not only be human casualties (cfr. the flood in 1953), but cultural heritage will suffer a considerable damage and loss.

Flanders lies above sea level, but still quite low, which makes it also vulnerable. Large pieces of the provinces of West-Flanders, East-Flanders and Antwerp are lower than 30 m above sea level. This may seem much, but a combination of low height with high tide and heavy storms can produce serious flooding, which can cause irreversible damage to heritage collections and buildings. In practice the cities of Bruges, Ghent and Antwerp are all three within the danger zone.

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Foto: Alex Tingle's Flood Map (2007) 

Many countries have set up flood maps and flood warning apps that you can find on-line easily. Alex Tingle, an ICT programmer, developed already in 2007 a flood map based on information from Nasa. The map is not correct because not all parameters were taken into account, and science has progressed a lot since then. Anyway it gives a rough idea how sea level rise affects countries. The map is interactive and the sea level can be adjusted. Is this a realistic picture? We do not know for sure but it is an exercise in learning what can happen. The absorption of CO2 by the oceans causes a rise of the water temperature. The consequence of this heating up is an expansion of the water volume, even if not a single drop of water is added by melting ice from glaciers or ice-caps. This means that the ocean level rises, and even if it takes a few hundreds of years before reaching the maximum expansion, computations predict that this phenomenon will be responsible for a sea level rise of 8m worldwide. According to Nasa sea level has risen 22,6cm from 1880 to 2013. And if Nasa’s projections become reality, sea level could rise another 90cm, maybe more by the year 2100, thus becoming one of the most important problems we have to face.


Foto: Nasa - Sea Level Rise

An important aspect of climate change is the expectation that the weather patterns will become more capricious. The effects will be different in different parts of the world. For Western-Europe extreme higher summer and winter temperatures can be expected, although cold winters will still occur. Weather phenomenons can become freakish, with periods of very intense rainfall alternating with long periods of drought. Storms can produce so much rain in a short time that rivers cannot swallow the water and swell to flood the country. Periods of intense drought can provoke subsidence leading to cracks in walls, letting water easily penetrate into buildings. For underground cultural heritage storage rooms this would be a nightmare.

Other aspects of climate change as a rise in temperature, raises the reaction velocity of chemical deterioration processes in cultural heritage objects and can stimulate mould development and the introduction of new harmful insect species.

How quick climate change will affect our lifestyle quite thoroughly we do not know yet. Will the change occur gradually or in jolts? How big will the impact be on Humanity and its cultural heritage? If the projected scenario’s of the International Panel on Climate Change and Nasa are correct we will be faced with the question in how far we will still be able to protect our cultural heritage. How will we tackle this problem, locally and internationally? Will we have to give up part of our heritage to save the most important sites and collections? Which ones will we choose to keep? Who will decide what to keep? Will we have to spread our heritage all over the world to avoid total loss?

It is five to twelve for our cultural heritage. Politicians, policy makers, curators, scientists and conservator-restorers have to think urgently about what we can possibly do. Just as in medecine prevention is of utmost importance here. We still have some time but we will have to use it usefully. Burying one’s head in the sand is no option. Sooner or later there will be a verdict. It is our responsibility to decide if we want a word in the matter or not.

Guy De Witte

All pictures are copyrighted unless stated otherwise.

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The fact that you read this blog shows that you are involved or interested in collection care and safeguarding cultural heritage. So you are just the public we are trying to reach: from professionals to private people interested in the Art of Conservation.

“We did not only inherit our cultural heritage from our ancestors, we are also borrowing it from our children”. This free interpretation of the quote “We do not inherit the earth from our ancestors; we borrow it from our childeren” and found originally in a slightly other version in a book of Wendell Berry:”The Unforeseen Wilderness: an Essay on Kentucky’s Red River Gorge”, is what it is all about. A responsibility and respect for our past, the delight of enjoying much beauty and the moral obligation to pass this on to future generations so that they can, with their own eyes, see where past, present an future merge together.

Maybe you will ask yourself “Why another blog/site about conservation?”. There are lots of good sites around from all kinds of organizations concerned with collection care of cultural heritage. So why this extra blog/site?

As co-developer and teacher of the “Cultural Heritage Staff Training”, organized by the Flemish Department of Education in Belgium I noticed that people have a constant and even growing need for knowledge about the “how” and “why” of deterioration processes, composition of art and cultural objects and assessments of materials and techniques. These are also the questions I continuously have. Therefore my aim with this blog is to provide more insight in the underlying science and scientific laws governing the survival of art and heritage.

In the 25 years I have been professionally involved in the field of conservation I have realized that safeguarding art and cultural heritage objects are a very complex matter comparable to a 3-dimensional building. Here we can consider all aspects of conservation as being in the horizontal plane, vertically linked to each other by the pillars of science as physics, chemistry, biology, climatology and a score of other disciplines working and interacting globally.

Conservation is not only a scientific and technical discipline, it is also an “Art”. For a good conservation empathy with a collection object or building is absolutely necessary. The feeling for the object, its composition, its history, its properties are a conditio sine qua non to achieve an adequate conservation. A boy of 7 years old, for whom I repaired one of his favourite books, called me his book doctor. This is one of the most beautiful compliments I ever received. Taking care of books is like taking care of people. Feeling out the patient or the object go beyond the necessary scientific discipline. Conservation is more than a profession, it is a way of life.

Want to know more about me? Just look at “About” or click on the following link


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