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19/03/2013

Preventive conservation of prints. Environmental, handling, storage and framing parameters.

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The subject of preventive conservation of works on paper, and therefore, that of prints1 is a very large and difficult one to approach lightly. This document must be considered as a brief introduction to the issue and the only aim is to provide a number of suggestions in a guide-like manner for creators.

The science of preventive conservation is a relatively new concept. It has been largely argued over by international bodies2 devoted to Heritage Conservation and Restoration since the early 1990s. Many definitions have helped widen the understanding of the term.

The most important matter of preventive conservation is to keep the works in a cool, not very humid environment since warm and humid environments favour the existence of micro-organisms – fungi and bacteria – and the spawning of insects. In addition volumetric deformations and modifications may also appear on the paper, directly affecting its resistance.  

Pollution, industrial gas disposal, car emissions among other factors, are quickly absorbed by paper in humid environments thus provoking harmful chemical reactions which are part of acidic elements working against the stability of the paper itself. Paper acidification is one of the most serious alterations, which must be avoided at all costs, since it affects paper by extremely weakening it, making it extremely fragile, friable and brittle. We must beware of the harmful gases that may be generated in the creation area of the pieces – solvents, varnishes, acids, etc. or fumes created by photocopy machines -.

The composition of paper itself has a few acidic elements such as lignin, which darken paper. The oxidation process speeds up when humidity concentrations are high or inadequate lighting is provided. Print works must be carried out on high-quality papers which should ensure stability3. These must generally be paper manufactured from alpha cellulose in pulp, free of lignin and other contaminating acids and should contain 2% of alkaline reserve in its composition. Many of the works nowadays, above all planimetric printing or works carried out without humidifying paper, - such as silk-printing or digital printing-. are carried out on unstable formats manufactured from mechanical pastes.

The excess of light radiation lead to a quick and irreversible damage and also favour alterations such as chromatic pigment modifications, photo-oxidation, paper yellowing and loss of colour among other damaging cases. Some elements included in the composition of inks such as pigments manufactured with metals – copper, cadmium, led, zinc, etc. – are sensitive to acid action, humidity and light. There is, therefore, a need to filter the harmful lights, above all ultraviolet rays (UV) as well as infrared (IR). It must be done so by fixing special screens on glass windows, skylights and doors4 and also include acrylic components in the framing system5. With regard to visible light, this must be of a lower level and the works should only be exposed for a few hours a day which will depend at all times in the sensitiveness of the exposed materials – there is a difference when lighting an etching illuminated by hand in water colours or a digital print and an oil ink; it is also different when lighting a very altered mechanical paper and lighting cloth paper with alpha cellulose and an alkaline reserve-.  

The ideal parameters for the conservation of prints on paper are the following:
Around 60% relative humidity, approx. 5% variation permitted and a temperature of 20ºC allowing a variation of approx. 2ºC.

Filtering UV and IR light. Visible lighting should vary between 50 lux for sensitive materials and 120 lux for stable materials. For a 300-hour daily exposure anywhere between 12,000 lux/hour and 40,000 lux/hour would be ideal depending on the sensitivity of the materials.

Avoid dust accumulation.

Keeping microbiological contamination under 1000 ufc/m3 of bacteria and 100 ufc/m3 of fungi in the air.
The main issue is to avoid serious variations in temperature and humidity levels.

Once we have all the environmental parameters under control, we must focus our attention on avoiding other type of alterations, which are direct consequence of the misuse of the print. That is why, the selection of the system and the materials for storage and handling processes are crucial. It is fairly important to make use of clean cotton gloves each time the piece needs to be manipulated. The transportation of the piece within the workshop premises must always be done in folders or between two hard6 bindings, which must be held by both hands.

If the works are not yet framed, the most recommendable action is to locate them in a horizontal archiving cabinet, which should include drawers and a skirting board of at least 15 cm high. The pieces of furniture must be located far from windows, high heat levels and wet walls. They must be stored at perfect levels, on surfaces which are free of movement and balancing and must be done so with inert and pest free materials. The print folders must be resistant to bending and oxidation and allow a certain level of air ventilation. The most appropriate ones are the ones made of steel covered in epoxy dust paint. The organization and placement of the prints inside cabinets is also an important matter. The conservation folder is the most recommendable system for the protection of works on paper because on the one hand, it can be seen, stored and transported without even touching the piece directly, and on the other hand, the framing, which isolates it from the contact of Plexiglas and protects it with a stiff stand on its back.

In the first place an appropriate ordering of the works must be done, keeping in mind the following criteria: size and conservation status. Same or similar-sized prints should be piled one of top of each other, always separating each of them by acid-free paper7. Prints in adequate conditions should be stored together or in the opposite case the prints that are in inadequate, fragile or in acidic conditions should be isolated. If the pieces so require, a system of individual and customized sizing protection can be used. The system can be manufactured from stable materials8. Single-piece storage not only physically protects the print, but also keeps temperature and humidity variations under control.

Framed pieces will be less vulnerable to alterations caused by the environment, if the framing is adequate, it creates another microenvironment which keeps it in a acid-free space which also helps reduce the effects of humidity, light and pollution. In addition to this, handling and exhibiting is made easier. With regard to the adequate framing system, you may refer back to a previous article9 included in an earlier issue of this magazine, which perfectly explains the materials which are most adequate, as well as the types of framing and protection levels required for prints. Developing in issues already mentioned is unnecessary although I would like to add a graph depicting the process and to recommend a system the author has named “Museum Framing”10 for all possible cases, however some exceptions must be taken into account. In order to obtain an appropriate fixed system of the works in the conservation folders I recommend using a dry system by using assembly polyester sheets known as conservation “Mylar”. I tend to suggest using acrylics instead of glass, because the damaging of glass can cause permanent damage to the prints themselves. I also support the assembly system with a frame once the back support is placed which would perfectly fit with the outline of the frame and would be at the same level of the moulding. I can only add that the alterations produced by an inadequate framing system are irreversible in most cases.

If the print is framed, it is ideal to hang it on racks in compact systems. The fixing of the works on racks, deposit cabinets or exhibition rooms must be done safely. These will be always fixed with two eye bolts located on the side mouldings of the frame – never on the upper moulding of the frame – and will be housed at the ends of the walls that will adjust to the weight and measurement of the piece.

A separate chapter will be devoted to cases in which damage is caused by accidents, the preventive conservation of books and print folders, the different transportation and exhibition systems of prints.



1 No description will be provided in this document on preventive conservation other than the one related to the paper format.  
2 The ECCO (European Confederation of Conservator-Restorers’ Organizations) provides a definition in its Annual General Meeting in 1993. The ICOM (The international Council of Museums) is currently working in a new version of the definition for preventive conservation, in order to include it in its ethical code.
3 All papers must comply with norm ISO 9706.
4 99% of UV filtering and 80% IR filtering and 2% reflection film.
5 Glass: Museum Conservation Quality. Acrylics: Optimum acrylic AR or Optimum acrylic Museum.
6 Any material in direct contact with the piece must have a neutral pH.
7 Neutral pH paper or slightly alkaline (with a 2% alkaline reserve of calcium carbonate).
8 Boxes, folders, binders, envelopes, acid-free paper cases or Mylar cases or Conservation polyester. The last two elements must always be provided with L-openings and low relative humidity.
9 y 10  Jiménez Peces, Jesús. “El enmarcado de conservación” (“Conservation framing”). Parts I and II. Grabado y Edición # 23, p. 54-60 and # 24, p. 54-60).

Bibliography

 

  • Forníes Matías, Zoel. “La climatización de los depósitos de archivos, bibliotecas y museos como método de conservación”. Ediciones Trea S.L. 2011.
  • Jiménez de Garnica, Reyes. “La conservación preventiva durante la exposición de dibujos y pinturas sobre lienzo”.  Ediciones Trea S.L. 2011.
  • Jiménez Peces, Jesús. “El enmarcado de conservación”. Partes I y II. Grabado y Edición nº 23, pág. 54-60 y nº 24, pág. 54-60).
  • www.aic.stanford.edu/sp/bpg/pcc
  • www.conservation-us.org
  • www.unesco.unesco.org

Photo :  © M.J.Montañés y Pedro R. Troyano

© g&e, Print and Art Edition magazine, article published in issue number 35 (print and digital). October 2012.

www.grabadoyedicion.com



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