• The weathering of tuff

    background, Restoration

    The increased usage of Ettringer tuff

    tufa capital at St. Stephen's church in Nijmegen
    danger of falling parts

    In the years I worked as a restoration sculptor I have often had to deal with statues and ornaments that originally were hewn in tufa and have weathered down over the years. In most cases, it was the so-called Ettringer tuff stone, which was used all over the Netherlands in the post-war years.

    At that time there was a huge reconstruction going on, and the traditionally applied tuf was hard to get or unaffordable. Even in Germany itself, where the tuff mainly comes from, there was a great need for good construction- and sculpture stone. The quarries could not keep up with demand.

    Ettringer Tuff -full-size sample
    Ettringer Tuff-sample at full size. large yellow bimsplaces and harder parts of. basalt

    Therefore, the choice for Ettringer tuff seemed an excellent solution: it was cheaper, it was available and in very large sizes to boot. The stone was somewhat coarser and had greater bimsspots (yellowish, sand-like inclusions), but it was easy to carve. For centuries sculptures and- stonemasonry had been made out of tuff and the rustic character of the stone fit well with the concepts of restoration at that time and thoughts about sculpture. Added to that, tuff is quite easy and quick to carve; it's not too tough when it's still fresh from the quarry.

    No dynamite, but moisture and temperature

    weathering of a tuff gargoyle
    Moss on a gargoyle, in a garden on the north

    Unfortunately, over the years it turned out that in many places in the Netherlands Ettringer tuff deteriorated very quickly, so much so that entire parts were falling down. For a time it was said that this was due to the mining in the quarries, without much factual knowledge. It was claimed that in the 1930s to 1950s the stone was removed from the quarry with dynamite and that this had caused hairline cracks that were now causing all the misery. However, that was not the case. It turned out that precisely this kind of tuff was particularly sensitive to changes in temperature and moisture.

    Volcanic ash

    Flowering moss at the head of the spout. This component is from around 1980
    Blossoming moss on the head, a part from around 1980

    Tuff is actually a rock formed from the ashes of a volcano. The volcano emits a heap of ashes- and grit particles, that eventually have to come down somewhere again. The coarse particles land closest to the volcano, the finer parts are blown further away. Thus, in a few days time a pack of ash and pumice and other parts can be deposited of even a few metres thick, just think of Pompei. Once the volcano has finally calmed down, the package is gradually condensed, and under the influence of seeping (rain)water, it hardens into rock. If the tufa is cut, the hard parts of basalt, the matrix of volcanic ash and the sandy yellow bims spots can easily be recognized .

    As with all types of stone there are types that are very suitable for finer work, parts or banks of inferior quality and unsuitable stone. The knowledge about this is often built up over centuries by quarry exploiters and stonemasons. As it turns out this Ettringer tuff is less suitable. Replacement tufa species such as good quality Römer- and Weiberner tuff are expected to last much longer.

    Shrinkage and growth

    weathering of tufa gargoyle made clear -1
    The legs are much older and begin to fall apart already

    Basically tuff is a bit like wood. If it gets wet, it expands a fraction. When it is dry, it shrinks again. Actually that applies to all stones a bit. But these tuff can absorb a lot of water and give it off again slowly. Added to that, the various components of the stone respond different to moisture, and that generates internal stress. All that expanding and contracting over time leads to fracturing, causing the moisture to penetrate deeper into the stone.

    Then there is the effect of temperature. Under the influence of heat the stone expands as well, and in cold weather it shrinks. That too gives tension differences and fracturing. The moisture penetrates deeper and deeper into the stone. If a frost period comes over it, that water freezes to ice, and ice of course expands, accelerating the whole process remarkably. Especially the slender protruding portions react to that first. Thus, it may happen that a church needs to place a fence to protect visitors from falling gargoyles.

    Solutions

    weathering of tufa parts from South Portal Stevenskerk
    When protruding parts are getting hot and cold all the time, and dry and wet, then these break first. Sheltered parts remain well much longer . Detail of the project at the South Portal of St. Stephen's Church in Nijmegen

    The solution in this case is very clear: patching will only help temporarily. For a while was tried to slow down the process by impregnating these sculptures in their entirety with acrylic resin under high pressure. Of these, there are by now many examples that show that this doesn't always turn out as desired, in tuff at least. You'll have to choose between letting the decline continue, whether or not delayed by fixing with mortar or something like that, protecting the original, or replacing.

    You can protect the statue by building a shelter or putting it inside, but usually it loses its accessibility or function in that location. For sculpture, frequently has been chosen for replacing. If the original is still somewhat presentable, you can for example display it inside, or put it into storage. That nearly stops the weathering process almost immediately . In that case, you'll have two statues: the original that's now inside, and a copy outside. Then the question remains how you want to replace it. Are you going to make a cast of the weathered image or carve a new one?

    Weathering of tuff stone gargoyle
    In wet conditions moss grows easily on it, after a frost chunks keep falling off

    I myself would of course (that's how biased I am) choose for carving a good copy in new stone. A casting is accurate, but it remains a cast of the already damaged statue, with missing parts and lost definition and all. A good restoration sculptor can fairly accurately recognize the various carving techniques and details and reproduce them, and thus do justice to the original intention of the sculptor who made it. I see it as the reperformance of a classical piece of music by a well-trained musician. Obviously you will hear something of the personality of the musician coming through, but in a good performance it will get to touch the audience. But in the case of a degraded casting, I'm not always sure about that.

    In the course of the years I have been carving copies of (originally tufa) sculptures in various types of stone. I have worked on copies in new tuff, in English portland stone, sandstone, basaltic lava and even granite. It all depends on the statue, the location, the speed of deterioration, colour, appearance and yes, also personal taste.

    Weathering of a gargoyle

    weathering of a tuff gargoyle
    Water penetrates into cracks, until the entire stone hangs together like a puzzle only out of habit

    In the photos of this post you'll see how quickly the weathering of a tufa gargoyle can happen at a high moisture load. There continues to be moisture in it, allowing moss to grow on it (volcanic ash is very fertile), and already within a few years pieces come down. The upper gargoyle consists of two parts. The bottom piece is probably from 1880

    Noah's ark: new in Muschelkalk limestone, old in Ettringer tuff stone. Tower of St. Eusebius' Church
    Noah's ark: new in Muschelkalk limestone, old in Ettringer Tuff. The yellow bims can clearly be recognized

    or even earlier. The (too large) head dates back to the early eighties of the twentieth century. You can see how the legs begin to fall apart, how the moss thrives on the head, how the neck is still relatively intact, and where the joint between the two parts is. This gargoyle was replaced by a sandstone copy earlier. Sandstone is very porous, but the moisture can very easily flow away again, and thus, it lasts for centuries. It is also insensitive to acid. Some types of sandstone are stronger than others; some kinds for example can't withstand wind erosion, or leaching of water, or contain too much clay, which again causes problems. There is almost always a good kind and a wrong.

     A work of art in Berlin

    Last week I came across an interesting article about a work of art in Berlin which uses precisely the properties of tuff: to react to moisture and temperature. With the accelerated decline of four huge stone blocks on four courtyards, this process of weathering of tuff is brought closer to the city dweller in an art project in East Berlin. These blocks are a kind of wells, which are fed with the rainwater from the roof. The article and the accompanying photos are well worth reading:

  • Teach New Restoration Sculptors?

    background, Eusebius, Restoration

    Today I found another video about the restoration out of St. Eusebius's Church in Arnhem (the Netherlands). It is a Gothic church that was richly decorated with sculpture – originally that is; a very large part of it has been rebuilt after the Second World War.

    To the first message about this restoration project.

    This video is about attention for the dying restoration profession, and it's also pointed out that there is no interest in the craft itself. It is always the question of 'the chicken or the egg': is there no interest in this work because there is no work in it, or there is a problem because we don't get any people who want to do it?

    Training sculptors?

    As for my own profession: so every now and then I get a request from someone who wants to learn this restoration sculpture, or from a sculptor who 'wants to do this work on the side'. But in recent years there has actually been no work and the four, five remaining restoration sculptors in the Netherlands (at least that I know of who do this work full-time) sat looking at each other waiting for a commission. It is not difficult to find interested people who want to learn the skill. More difficult is to find people who are both dexterous, as well as talented, who have a sense of shapes and forms, and are physically strong, as well as able to make a production, and finally want to continue to do this for years. But that's all still not too difficult; there just needs to be enough work.

    Actually I noticed of late that this profession is so diverse, and that it takes quite a long time before you've mastered all kinds of aspects. You can keep learning until your eightieth birthday.

    Seven years training

    I recently talked with the owner of a major restoration stone masonry firm about education, that it easily takes half a year before a student starts to produce a little bit. 'Half a year?’ he said, 'I'm counting on seven years before anyone is well versed in this work!’ And that's about right. In Germany you must will need to complete four years training and work as a stonemason, before you can start training as a sculptor. I believe the training as a sculptor then takes another six more years. Even the masons and carpenters in restoration were talking about seven years before someone can work well independently, which matches very nicely the standard of 'it takes 10,000 hours before you can master a topic or skill'. That is nearly impossible for a small company to do.

    There is no point in training some new sculptors every few years when it's already clear that there will be no work for them afterwards. So the conclusion of the video is exactly right: It's a dying craft. But that is simply because there is not enough work. As my generation ceases working, I fear that one will have to go abroad for these items, where the supervision of the quality is less and consultation more difficult , and a piece of knowledge gets lost, unfortunately.

    Batavia

    In 1985 the construction of the Batavia ship was begun in Lelystad. It was a learning- and training project that in many ways an example could have been an example. People were trained in various disciplines, including wood carvers. But if there is no further employment after such a wonderful project, then the effect of the entire program will evaporate again within a few years. The only thing that could provide a stable knowledge base (something that I don't control myself) is a cultural change, which provides new employment for people practicing those 'old’ crafts. For example, that it would be quite common again to decorate buildings with sculpture, or that a sudden demand arises for religious statues, for example. The model of the Batavia would then certainly be usable , and I have long dreamed of making beautiful things together with enthusiastic young people. Maybe we'll see that happen one day!

    Update 19-08-2015:

    Another video, in which the workshop near St. Eusebius's Church can be seen. Among other things is shown how two stonemasons work, my colleague Stide Vos is copying a tuffstone dragon in Muschelkalk, and at the very end I'm flashing by for about 1 second. Unfortunately, we are mentioned as students, but the moment we can go train new students has not yet arrived. It would be a pity if with our generation (Stide and I in our fifties belong as I believe to the 'cubs' of the restoration sculptors) the skill would die out in the Netherlands. With enough work it would also make sense to now start training the next generation.

    Would you still love to learn classical sculpture? In Amsterdam is there then Figura-Dutch Academy of of Figurative Sculpture, where part-time training is given and individual shorter courses can also be taken. In Antwerp There was once part-time stone training- and restoration sculpture (recommended), but since the change of teacher, this program has ended.

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