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Transporting pastels to exhibitions

19 October 2017

Here now is the second of my talks given at the seminar Le Pastel: regards croisés sur une technique singulière on Tuesday. As before you can find full references, bibliographies etc. for the talk in the online Dictionary of pastellists, and in particular in the Prolegomena. An earlier post is also relevant. As with all posts on this blog, these are personal opinions.


Let us now turn to the issues raised by moving pastels.

I’m not going to take you through the long history of pastel damage. You can find lots of examples in my Prolegomena: Rosalba writing about broken glass; Oudry sending a picture to comte Tessin in Stockholm, with instructions to open it to remove all the pastel that would surely be found on the inside of the glass. You may at the end of this talk have some sympathy with the Duke of Hamilton who insisted that a pastel be carried 40 miles to his palace “on a man’s back”, although museums aren’t allowed to do that now.

The basic position in museum policy remains that “unfixed pastels are usually too fragile to travel.” This was formalised as far back as 1963 in a Unesco document, and it has been reiterated for example by the loan principles agreed by the Bizot Group of leading museums worldwide. It remains the standard position of most of the major museums who collect pastels.


But nevertheless we have to discuss the matter because several recent exhibitions have been promoted on the basis that the technical issues of transportation have been solved: here for example is the promise of “safe handling…through advances in methods of art transportation”; I want to challenge that claim.


You may say that large numbers of fragile works of art are being moved all the time, and you rarely see any evidence of damage: we shall see that that is to misunderstand the problem. Some people suggest that the risks of damage are outweighed by the scientific value of showing these works which would otherwise rot away in store rooms. But that isn’t how the issue is presented to lenders or museums when they approve loans. You can’t take calculated risks when you can’t calculate the risk.

During this talk I want to identify some of the biases and other cognitive errors that endanger the debate. You’ll hear later on from people involved in the scientific attempts to find solutions, but I want instead to illustrate the problem from a practical viewpoint, and I shall draw learnings from the worlds of finance, insurance, medicine, sport, natural disasters or even food logistics to inform or illuminate the discussion.

The first thing we should note is “survivor bias”: because the pastels that we study today have survived in good condition, we ignore the ones that are unexhibitable or destroyed.


The fact is that a great many pastels have suffered damage. Often we don’t know why or when or how, but we do know that it has happened. One wonders what happened to the Liotard of Lord Mountstuart at the Getty when we compare it with the replica kept safely by the family. We simply don’t have the information to say what caused the losses (the degradation was evident before the pastel left Scotland for Los Angeles, presumably by air), but we can wonder if they had anything to do with the fire which destroyed Mount Stewart in 1877, which at the very least would have required hasty evacuation.

Damage is surrounded by a wall of silence from owners and museums, fraught with conflicts of interest and covered in a veil of ignorance, as we still don’t know the exact mechanism of why pastels degrade.

Proper risk management tells you not just to look at the probability of an adverse event, but to multiply that by the consequences. That is why a pastel is so much more in danger than an oil painting. The response can be highly nonlinear and disproportionate. Think of a haemophiliac child: it’s not that he’ll fall more often than a normal child, but that if he does, the consequences are life-threatening.


A good example of this principle is when it comes to glass breakage. This is one of the biggest hazards for pastels, with far more serious consequences than for oils. Note too, since paintings usually weren’t glazed in the 18th century, any glass they have now is toughened and less likely to break. So the experience derived from moving oil paintings can give false confidence.

Pastels with broken glass appear frequently, not only in the saleroom. You can even find the frame falling apart with poor handling: joints opening, or whole sections dropping off.

The routine way to protect glass in transit is to tape it. As you can see from the picture, this doesn’t even protect the pastel. But as we now know, you mustn’t tape the glass of pastels as it creates static electricity which can lift particles of pigment onto the inside of glass.

In fact this transfer can also arise just from cleaning the glass – particularly if you’ve decided to mitigate the breakage risk by adopting one of the new specialised glass replacements: if you don’t clean them very carefully, so-called low static glazing can easily become fully electrostatic.


This SLIDE shows how this phenomenon occurs differentially with some pigments, in this case white: nothing is visible when the glass is removed and laid down against a white background, but against black, you can see that the transfer from the pastel it covered occurs up to edges in a way that shows it isn’t contact transfer. We just don’t understand the phenomenon fully.


Pastels are astonishingly easy to damage by poor handling once out of the frame. Unprotected backs can lead to smudging or tears. I’ve seen hundreds of tell-tale fingerprints near the edges: they are the pastels you don’t see in museums or exhibitions. This can happen in the auction room: dealers with little intention of purchasing insist on seeing them out of the frame. Also in the photography studio, dazzling lights increase the accident risk, and can even melt pigments.

But when they get to the framers, there’s a hazard most people aren’t aware of.


This is what the gesso room looks like. That white dust gets everywhere, and if you are mad enough to unseal a pastel anywhere nearby, it will soon be covered in this stuff which can never be removed. And even the most talented carvers and gilders are quite capable of screwing the fittings too tight, and shattering the glass a second time. Worse: some will resort to powered ratchet screwdrivers to do so. Which is what unsupervised logistics staff routinely do when your back is turned: they simply think you’re being fussy in asking them not to.

When we run through the standard insurable risks, pastels fare worse than oils because of disproportionate consequences. Thieves are unlikely to take the care required for pastels to survive undamaged, particularly if they remove them from the frame.

In a fire, pastels can be damaged beyond repair without the flames reaching the work, as was accepted in a law case concerning a Degas pastel of Grecian Dancers. The court accepted the evidence that-

The heat and the humidity had caused molecular change, the effect of which depended on the extent of the heat and the humidity. In simple terms, he [the expert witness] considered that the heat and humidity were similar in effect to an oven and the crystals were cooked and became like flour; in consequence, they lost their adhesion and shine…  Loss of adhesion: The pastel appeared in good condition, but with time each particle of pigment would fall away. He did not consider that long term damage would have been visible in 1995 [four years after the fire]

To prevent fire museums have sprinkler systems. They can be faulty: when the Mona Lisa was lent to the Met in New York in 1963, it was drenched by such a fault. It survived; a pastel would not have.


With flood, the risks are obvious, and infinitely more severe for pastel than for oil. Even condensation from humidity can cause irreparable water marks, especially on external walls. Don’t assume that museums are immune from this: here’s a major American museum which can’t control the moisture levels outside or in. And at the opening of the La Tour exhibition at Versailles in 2004, on a very wet day, humidity rose to an unacceptable level as the guests streamed in.

[SLIDE omitted] Worse than a damaged pastel is a badly restored one.

But unquestionably the main concern with pastel transportation is the issue of shock and vibration. From the earliest days of pastel people have tried to remedy this inherent defect of the medium by devising various methods of fixing. These were rarely successful, and it’s far from clear that fixing applied 200 years ago is still effective. But the price was too high.


You can see the change in colour from Cotes’s Chambers, which Russell wrote about and of which he probably made the copy that shows the original colour. Worse, you can get unsightly tidemarks, as in La Tour’s autoportrait. This is just one of many examples of ill-thought-through attempts to manage risk: we may even term this “iatrogenic risk”.

So what happens when an unfixed pastel is moved? We often see reports from museums that “condition checking before and after the journey indicated that there was no visible change to the work”: in other words, they’ve completely missed the point. Damage doesn’t usually result in a neat pool of powder resting on the bottom spacer which you can photograph to support a claim from your insurance company. In any case most insurance policies (including the UK Government Indemnity Scheme) offer no cover for “inherent vice or a pre-existing flaw”, which probably excludes this sort of damage even when it is visible. This is an area that is rarely discussed with lenders: if a pastel does suffer damage during transportation resulting from its friable nature, both lender and borrower may be in for a surprise. However extracting claims data is extremely difficult, even when requested from public institutions covered by the Freedom of Information Act.

Instead of the heap of powder you get at most a subtle alteration of luminosity that results from alterations to bonding at microscopic level (as the court found in the Degas case). Generally this is imperceptible. This invisible damage is one of the most important features of moving pastels. It is exacerbated by data bias: older photographic records are often too poor in quality to reveal the deterioration over time or link it to specific traumas. This is also made worse by damage denial or the causal-immediacy problem: people who don’t believe there’s anything wrong continue moving pastels. This is like boxing where a doctor examines the fighter after each match and can’t see any damage, but a decade later the cumulative brain damage becomes evident.

You can find exactly the same cognitive errors in financial markets and even with natural disasters. There is “ostrich behaviour”, where we simply don’t act on theoretical risks; “optimism bias” where we don’t take precautions believing that “it wouldn’t happen to me”; “single action bias” where implementing one precaution means we don’t bother with the others that are equally important. And “amnesia bias”: even after a catastrophe, the measures we introduce to prevent it are forgotten after a period.

But if you must move a pastel, what is the best way to prepare it for transportation?

The first question is whether to open the pastel. This is where the gap between protocol and practice can be biggest. If you don’t open it, you have no idea what’s inside: you just hope for the best. The tension of the canvas may have gone, so that if they are tipped forward the pastel will touch the glass. The spacing is usually too small. Worse, you can’t check whether the spacers are secure or liable to fall during the journey potentially destroying the work. That isn’t solved by travelling horizontally, as they can still slide across the surface.


There’s an even worse hazard, with works on multiple sheets where the paste has dried out and the paper starts to slide.

But if you do open the pastel, you not only break the integrity of what may be an original assembly, you greatly increase the risks of accidental damage. Where do you cut the backing seal safely when you don’t know what’s underneath? I’ve even encountered cases where the spacer is glued to the front of the pastel and glued also to the glass: a nightmare to open safely.


Travelling without glass raises other problems. How do you transport the unframed pastel in a dust-free environment and secure it so the surface can’t make contact? A method that effectively clamps the edges may be placing strain on the weakest spot of the pastel. But there’s an unexpected issue that emerges from recent research on the vibrations of canvas: the assembly with backing board and glass provides a very significant additional level of protection from vibration. So by trying to solve one problem you exacerbate another.

And if instead you decide to replace the glass with toughened or laminated glass, the extra weight itself can weaken the frame and increase shock levels.

The next question is what type of packing to use. Some institutions are still using large triple-lined museum cases, with up to five pastels in a case, ensuring that the boxes are too heavy to move without hydraulic equipment which itself creates vibration.


One danger is that too much packing can create an illusion of protection: it’s like boxers practising in safety helmets which have now been abandoned since they have been found to cause greater long-term damage than unprotected sparring. Twenty years ago research showed that a double case was preferable to a triple case because it was lighter, and because the foam insulation can’t be optimised for all levels. But even a 50 kg case still needs mechanical handling. The same problem can arise with clever ideas such as transport at 45°. The obvious logic is that a single case is even better.

But you need to be careful that using the lightest possible case to mitigate shock may make it harder to buffer the humidity and temperature levels adequately. These are always mentioned in protocols, but what is actually done in practice to manage them? The answer is often very little.


Yet as we know this is why joints in frames open up. And what you may not have thought about is that the same thing happens to the pastel strainer. Even if it doesn’t cause failure, warped strainers show as cockling at the corners. Unlike an oil on a stretcher, there’s nothing you can do when the pastel strainer loses tension; relining or transfer to another secondary support is always hazardous. Pastels are more likely than oils to be oval, which makes these problems worse. The impossibility of cutting the wood along the grain more or less ensures that the joints will open up, of both frame and strainer. And original glass ovals are cut by hand: their entire weight can rest on just a few sharp points, so they are hugely vulnerable to breakage from shock transmitted through the frame.


As for the transport vehicle, so-called air-ride suspension involves tail-lifts (image left) which need the engine to be running when the vehicle is stationery: you don’t need a meter to detect unacceptable levels of vibration from these.

You will say that this is mitigated by using the right kind of foam (image right). But there is still no consensus as to whether this is soft polyurethane or polyethylene such as Plastazote. And you very rarely see anti-static foam used (it is usually produced in a “shocking pink” colour), although it is close enough to triboelectric materials even with a framed pastel to make investigation into this hazard worthwhile.


Here’s a simple experiment that I did with a wooden frame supported on a standard foam, repeated by driving over the same stretch of road a second time with the addition of very soft alveolated polyurethane. This was in a passenger car which actually has far lower vibration levels than larger vehicles. You can see that the shocks were damped – by perhaps 30–40%. Incidentally the highest peak while the car was moving was when I drove quickly past some road works where a pneumatic drill was being used. These are the things you can’t control. Also getting the picture into or out of the vehicle involved the biggest shocks. We just don’t know what the trade-off is between a few big initial shocks and lots of little ones, or between shock and vibration. (That’s why experts don’t even agree about road versus air.)

We should note here “science bias”: because dataloggers conveniently collect shock levels, we assume that is the only danger: vibration is harder to record. But because there’s something which can be measured, we ignore factors that can’t. We test one modern sample, and extrapolate to the behaviour of works created 300 years ago with quite different materials. Bad science should not silence common sense.

Common sense does however tell you that when a heavy case is dropped, the energy has to be dissipated somehow, and there is a risk that some ends up at the molecular level weakening the bonds that hold the pastel together.


But the most comprehensive research on moving paintings shows that damping solutions simply don’t work, and in many cases magnify the input vibrations without reliably attenuating output. Mixing layers of foam of different hardness can’t overcome the issues. We haven’t really progressed fundamentally since the Heath-Robinson approach taken for the transport of the Saint-Quentin pastels 100 years ago: we have merely added a bit of foam here, an air-bag there like the wheels-within-wheels of Ptolemaic cosmology before Copernicus. Shock levels from road transport simply can’t be eliminated. They are always worse than the flat zero line for leaving the pastel at home.

There’s even the risk of contact between pastel and glass if the canvas tension is too loose or the space too small. When I raised this with the organisers of one recent exhibition, the response was to insert wadding beneath the pastel. But this led to polyester being placed in direct contact with vellum, despite the fact that this combination is known to generate static electricity. Another example of a poor solution creating new risks.

One of the difficulties here is the reluctance to share experience. I had to use the Freedom of Information Act to find out if pastels sent to a recent exhibition travelled horizontally or vertically, and had to pursue the process to appeal. Even when it comes to a description of the protocols and techniques people are developing, you can encounter a wall of silence.

Apart from the question of vibration, and assuming your pastel has arrived at the exhibition location unimpeded by fire, flood or theft, is everything then OK?

Not necessarily. One possible problem which I’ve never seen discussed (and may take on a larger dimension post-Brexit) concerns customs clearance. Government border agencies have extensive rights to examine any object crossing borders to safeguard against illicit substances, be they explosives or drugs (couriers may not always be present, particularly at airports where cargo handling takes place in secure areas). It is difficult to imagine that should their attention fall upon a pastel, they would bring the necessary skill to investigate it safely.

Your pastel is likely to arrive some weeks before the show. Where will it be hung temporarily?


Many museums continue to use moveable storage racks which create appalling levels of shock/vibration, not only when the pastels are viewed but when nearby pictures are taken out. Even fixed racks are often sufficiently near moving racks to be affected by the vibration.

Have all the other exhibits been put in place first, and all necessary holes drilled? Are you going to fix new hanging furniture to the back of already weakened 18th century frames, and will the staff remember to screw these by hand? Will all the pastels be moved by hand, or might trolleys be used (if so even the pressure of the tyres is an issue that has been investigated)?Slide48Or maybe this type of machine is to be used with larger pastels? When the pastels are unpacked, will all the best efforts of the transport protocol to ship at an angle of 10°, 45° or whatever be undermined to get the work out of the box?


Aren’t they in fact often turned over when wrapping, directly contrary to most instructions? Are the pastels to go on temporary partitions or display stands which may be subject to floorboard vibrations? You might think I’m exaggerating, but footfall on parquets from groups of visitors was a sufficient hazard to oil paintings to be the subject of specific investigation with shock levels akin to transport.


More so is the possibility of the institution hosting concerts in nearby galleries with loud music: there’s even an hilarious video showing the “Met Workout” – gymnastics classes held in its galleries. The Louvre also hosts these. Vibration levels from a Formula 1 event held in Trafalgar Square in July 2017 were sufficient for “steps [to have] been taken where necessary to remove items from display” according to minutes of the next board meeting.


Lighting is perhaps the one area where almost all museums understand the dangers. It’s in fact more of a problem for watercolours than for pastels. But it is certainly an issue, as you can see from comparing both versions of the maréchal de Saxe’s green uniform with the print showing the proper colour of his uniform; or Lady Berwick’s red elbow hidden by the frame. And you need to calculate the exposure not just for opening hours, but special events, set up and even cleaning.

Even the installation of exhibition lighting can be a risk to the exhibits. Official loan standards recognise this, recommending that the lighting be installed before the exhibits arrive to minimise the risk of damaging objects that are being installed; but these guidelines are routinely ignored. This is understandable for pastels since their uneven surfaces are exacerbated by raking light, so adjustments after they are hung are often required.


And when the doors close at night, there’s the housekeeping to worry about: floor polishers vibrate and can easily touch the skirting. Even the dusting should be done by hand, not with a vacuum cleaner.


Finally the biggest risk is often when the exhibition is being dismantled. All the best laid plans can be put aside in the confusion which, for the exhibition where this painting was smashed, was described as “pandemonium” by a trustee of the institution concerned.


So to summarise. Pastel damage is a real problem. Whenever you move a pastel, you put it at risk from a large number of hazards. And the evidence is before you if you look for it of pastels which are dull or used, if not completely ruined, where by far the most credible explanation is transport.

Let me offer two suggestions. The first is a test as to whether the science of pastel transportation has reached even a basic level. The test is this: what is the equivalent of a single 10g shock, such as you might get in an airport cargo handling bay, in terms of shocks of 1g from air cushioned road travel? Demonstrating a clear answer to that question seems to me basic.

Second: all responsible museums arranging to borrow or lend pastels should insist on taking and publishing ultra high resolution images of the pastel before and after each leg of the journey and return. Only thus can we begin to identify when damage occurs.

Both of these ideas are necessary for progress, but not in themselves sufficient to support the contention so complacently displayed in the Royal Academy at the start of this talk.

For centuries pastels were protected by being too unfashionable, too boring to be borrowed. They moved only when people died, and even then not always though the salerooms. The lending exhibition is broadly speaking a recent phenomenon, and is putting our pastels through a trauma that may take many years to reveal its consequences fully, when it will be too late to reverse. Our biases and prejudices blind us to these risks just as President Trump denies climate change. Of the impact on our pastels from this revolution in museology, it is still too early to judge, in the rather wiser words attributed to Zhou Enlai.


From → Art history

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