Go back to article: Doping at the Science Museum: the conservation challenge of doped fabric aircraft in the Flight gallery
Current conservation of doped fabric
The specific context in which a conservation decision is made is very important since it is what will ultimately determine the final outcome of the treatment. Factors such as the particular history of the object, the prevailing philosophies at a particular time, the reason an object is receiving conservation, the ethos and aims of the owners, the training and skills of those involved and resources available will vary between projects and influence the approach taken. It is therefore impossible to provide a definitive ‘correct’ approach. The following discussion, instead, presents several options available to manage the conservation of doped fabrics, and an evaluation of their potential strengths and weaknesses from a museum conservation perspective.
From the examples that are available within the literature and examples of ongoing projects, it seems that re-covering of aircraft was historically the most common approach within museum collections and remains a viable option now (Mikesh, 1997; Firth, 2009). This practice, whereby the old material is removed and replaced with new, ensures that objects have a high aesthetic appeal in that they do not show signs of wear and tear or damage, and are ready for public display.
Re-covering also provides an opportunity to examine the interior surfaces and parts of an aeroplane, where other forms of deterioration may have taken place unobserved beneath the doped fabric covering. The removed material, moreover, may be easier to handle, pack into a smaller space and store in more controlled conditions, compared with when it must be maintained in situ on the object, and so there is the possibility that the material can be preserved for much longer out of context, and made more easily available for research projects and study.
The process of re-covering, however, raises a thorny issue in conservation discussions as to the distinction between a restoration and a conservation approach, and whether such a major intervention necessarily fits as a conservation treatment. The distinction between conservation and restoration can be subtle and hard to clarify, but probably comes down to a matter of approach and how the aircraft is re-created and reinterpreted before, during and after the treatment process (Staelens and Morris, 2010; McManus, 1994; Horelick, 2015; Croker and Kemister, 2009).
In a conservation treatment, one of the most important aspects is not necessarily the actual physical work done to the object, but the work that goes into understanding the object in terms of what are often described as its tangible and intangible values, or its significance (Australia ICOMOS, 1999; Wharton et al, 2011). This relates to understanding how and why an object is important in terms of both the physical materials from which it is made, and the more ephemeral cultural or social ideas that may be associated with it. It is only through understanding these ideas that an informed conservation plan can be agreed, in which it is recognised that conservation will at once enhance, but also potentially destroy, certain values associated with an object (Odegaard, 1995).
Removing signs of damage from an object, for example, may restore a previous aesthetic appearance, but simultaneously it removes a part of that object’s history, namely evidence of the fact that it was damaged. It is only through understanding how and why the damage occurred, and how this relates to other values held about the object, that its contribution to our interpretation of the object can be properly understood. A conservation treatment, therefore, may well resolve that retaining signs of damage is in itself a good thing.
A restoration treatment, in contrast, will potentially start from a very different conceptual understanding of the object, in that it will seek to return it to a perceived earlier state, and this concept of the object’s earlier form will take primacy over all other considerations. There will not, therefore, be the same attention paid to trying to understand the object as fully as possible and explore alternative treatment options beyond this one interpretation. The key difference from conservation, therefore, is not that the actual treatment will necessarily be different, but rather lies in the paths and decision-making processes used to reach that final treatment decision (Vinas, 2005, p 27).
A re-covering, therefore, needs to be very carefully thought through and justified if it is to be an effective conservation treatment, as opposed to a restoration, and there are a number of dangers that need to be considered. The desire to source historically appropriate materials, and carefully re-create original stitch patterns for example, may, counter-intuitively, be problematic since the production of aeroplanes was not always of the highest quality or standard owing to variability in production and manufacturing.
Painstakingly re-covering an aircraft, therefore, attempting to get every single detail perfectly correct and looking pristine, risks losing the very idiosyncrasies and imperfections that perhaps made the object unique and gave it its identity. The end result, therefore, is an idealised object that has, for want of another word, been made ‘better’ than it ever was in previous incarnations. This would be classed more as a restoration and not a conservation, since the focus is on returning the aircraft to an earlier form, even though in this case it never actually existed, without adequately thinking through what this might mean for a viewer’s interpretation and understanding of that particular object.
There are, in addition, a number of practical considerations that may limit the desirability of re-covering in certain contexts. Practically, it requires a large enough space in which to work, and a doping area fitted with special ventilation and environmental control systems for health and safety purposes, as well as to control the dope drying process. Sourcing materials representative of those being replaced can be a further difficulty, and finding staff with the required skills and knowledge can also be challenging. The process of re-doping, moreover, presents potential danger to the underlying frame. Excessive shrinkage can occur in the doped fabric which may distort other parts of the object, and there is anecdotal evidence that cellulose acetate butyrate dopes in particular can continue shrinking long after the initial application (Pearce, n.d.).
An alternative, less interventive option for dealing with tears in the fabric of aeroplanes is to cover the tear with a patch of material, and then secure this in place with several coats of fresh dope.
© Science Museum/Science & Society Picture Library
Doping a new patch into place to stabilise a tear in the upper side of the Hawker Hurricane (object no. 1954-660) wing.
Depending on the quality of the treatment, this approach appears to result in a strong bond between the patch and the area around the torn doped fabric surface, and so prevents further growth of the tear. The tautening effect of the dope used in the repair also maintains the profile of the wing as it restores the stretched, smooth profile, which may be lost owing to the release of tension when the tear occurs. It is, finally, a simple, easy method that requires relatively few resources, and can result in an aesthetically unobtrusive result as the new materials match the original but can still be distinguished from the original on inspection. It also maintains traditional skills and knowledge regarding the maintenance of historic aircraft.
The use of doped patches, however, can also cause further problems. The shrinking of the doped patch introduces more strain into the material, which may simply cause the doped fabric to begin tearing in a new area – a result which is unacceptable for a conservation treatment. The use of patches, moreover, can become very aesthetically distracting if there are many areas requiring treatment, and a surface may end up resembling a patchwork quilt rather than a smooth flying surface.
© Ben Regel
Underside of the Vickers Vimy (object no. 1919-476) showing numerous patches applied during conservation.
Applying and removing a doped-patch area, moreover, without significantly affecting the underlying doped fabric surface of the aeroplane, is almost certainly impossible as the solvents used in the fresh dope will probably have an effect on the underlying surfaces of the museum object. This is very important to conservation treatments since the idea of reversibility or re-treatability, whereby any conservation work should be removable from the object without significantly altering the object that is left behind, is a core concept that helps inform many conservation decisions (Lambrinou, 2010).
In order to further inform this aspect of the treatment, however, much better knowledge is needed about how different conservation materials might react and behave when left in long-term contact with doped fabric. The ideal would be to find a material that could be applied in a form that would not chemically interact with the underlying substrate, and would still be removable at a future date without causing significant change to the original doped fabric material.
Aside from the idea of reversibility, another key concept for conservators is that of minimum intervention. This idea states that conservators should only do as much intervention as is required for the desired outcomes. In this particular instance it has already been discussed how the patches are effective at achieving the required outcome of stabilising the tear, but there is a question whether they are still too intrusive. It is not clear, for example, that it is necessary to cover the entire area around a tear with a patch or if alternative, smaller repairs might prove just as effective at preventing tear growth. Understanding of the forces acting on the tears, therefore, and the strength, position and size of any repairs necessary to effectively stabilise these forces would be required to adequately inform this part of any new treatment proposal.
Caution must also be exercised in using modern commercial dopes, since they are proprietary formulations and not all the ingredients are known. This is obviously a problem in using any proprietary conservation material, but is especially true at present for modern commercial dopes as there has been so little study of their short- or long-term behaviour as conservation materials. Their compatibility for use with other dopes, moreover, should not be taken for granted.
Alternative patching materials have been investigated at the Science Museum in a student project undertaken on the Vickers Vimy (Beesley, 2009). This sought to test the efficacy of materials already well known within the conservation profession, such as Beva 371 (unknown proprietary formulation) and Lascaux 498HV and 360HV (both acrylic polymers based on butyl methacrylate). Unfortunately these repairs are showing signs of failure where they have been put into practice, indicating that either the materials or techniques used to apply them lack sufficient long-term performance in this context.
Component DOI: http://dx.doi.org/10.15180/160605/012