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Museum Conservation Materials

By Peter Winsor and Stephen Ball

The individual fact sheets in this series make frequent reference to 'conservation' or 'museum' quality materials for cleaning, protecting and wrapping objects. This sheet provides more information about these products and materials, and explains what terms such as 'acid free' really mean. A list of UK suppliers is included at the end. A more comprehensive list will be found in the Museums Yearbook, published by the Museums Association.

Always use archival quality materials on or close to objects. ('Archival quality' is a non-technical term implying that materials are both durable and chemically stable.)

Wrapping, Boxing and Protecting

'Acid-free' paper and board

The term 'acid-free' has become a familiar label for book papers in recent years, but what does it mean? Cellulose fibre pulps derived from wood or cotton are naturally acidic, a quality associated with continuing chemical activity. Tissues and other papers derived from these pulps degrade over a number of years unless the acidity is neutralised. Acid papers yellow and become brittle and weak, an effect that appears in a few hours if newsprint is left in bright sunlight. Clearly, such a reactive material must not be allowed to touch valuable objects in the museum. Paper manufacturers neutralise the acids with a chemical such as calcium carbonate.

This is a broadly effective process but has limitations. First, because the pulp is not naturally pH neutral but chemically buffered, the natural acid in the paper will reassert itself over a period of years. This process is aided by the absorption of acidic pollutants, and returns the paper to an acidified state that once again threatens nearby objects. Paper and board can also become acidified by the action of residues of chlorine from bleaching and aluminium sulphate from sizing.

Second, some 'acid-free' papers and boards are overbuffered to an alkaline condition, usually pH 8.5 rather than the neutral pH 7.0. These alkaline papers could be harmful to some types of objects. To find out precisely what type of 'acid-free' product you are buying, read materials catalogues carefully and ask the supplier if you are in any doubt.

The best quality wrapping papers and boards for boxes and framing are naturally pH neutral, and remain acid-free for much longer. Some of these products are made from cotton rag and others from abaca fibre, which is derived from the Manila hemp plant (Musa textilis). The hemp-derived type is normally the only paper or board recommended for use with more sensitive items such as photographs and textiles, and is much more expensive than buffered materials.

In most other cases it is safe to use the much cheaper buffered type of acid-free wrapping papers, mounting boards and boxes, though many museums replace wrapping tissue every five to ten years.

'Traditional' types of wrapping paper are not necessarily safe. IN particular, the blue tissue paper used in the garment trade and clothing shops is quite acid and prone to transfer its blue colouring to the textiles it is supposed to protect.

Calico Cloth and Unbleached Linen

Calico and linen are light fabrics available from haberdashers. The material should be unbleached and untreated, and is washed to remove size, proofing chemicals and other unwanted substances. It is then suitable for covering textiles, racks of hanging costumes and other objects in store. Cloth covers provide a cost-effective way of protecting objects from dust and snagging. Wash the covers regularly - at least once a year. Avoid washing products that contain brighteners, bleaches or enzymes that could leave residues, and rinse thoroughly.

Charcoal Cloth

Charcoal cloth is one of a range of materials that actively absorb atmospheric pollutants such as acetic acid, formaldehyde, hydrogen sulphide and ammonia. These substances are particularly harmful to textiles, polished metal surfaces and works of art on paper. The 'activated' charcoal responsible for the absorption is sandwiched between layers of fibre, and the resulting material can be cut and sewn like cloth.

The cloth is cheap, very easy to use and effective. It is available on rolls and as made-up bags. Like buffered acid-free tissue, its power to absorb is finite, so it must be replaced at intervals with fresh cloth. Use it inside the backing board of framed works of art, or to line display cabinets and storage boxes to neutralise harmful vapours given off by fibre and particle boards, new wood, and painted or treated surfaces.

Tyvek

Tyvek is the trade name for a spun-bonded, non-woven, high density polyethylene fabric. It is non-abrasive, waterproof, rot-proof and dust-proof. Its original conservation use was for labeling objects from archaeological excavations, but its range of application has extended widely to include individual coverings for textiles and other objects, and 'indestructible' mailing envelopes. Tyvek is available in wide rolls and as label tags, with or without perforations.

Polyester Film

Polyester is the most generally useful of all plastic fims used for long term storage. Frequently appearing under its common trade names of Melinex or Mylar, polyester film is usually the material of choice for preserving documents and photographs. It is crystal clear and chemically stable, and contains none of the fillers, plasticisers or other additives present in many other plastics. It is these additives that deteriorate or leach out, causing damage to sensitive objects.

Polyester film is available as cut sheet or rolls, and in a wide range of made-up sleeves and envelopes. For museum use choose welded rather than glued seams; for some purposes an unsealed four-fold design is best. One of polyester's advantages is that with the aid of the right equipment it can be heat or ultrasonically welded, which makes it ideal for the encapsulation of documents and ephemera.

Polyethylene Film or Sheeting

Bags, sleeves and envelopes made from polyethylene film are a cheaper alternative to polyester enclosures, and will protect ephemera and matted prints or photographs from dust, abrasion and fingerprints. Polyethylene is not as tough or stable as polyester, and the film is not as crystal clear.

Plastazote

Plastazote is a dense, inert polyethlyene foam that is available in a range of densities and thicknesses. It contains no harmful additives and the foaming agent is ozone-friendly. Use Plastazote to line drawers, cabinets and cupboards to cushion objects for storage or packing. Holes and recesses can be tailored to the contours of the object with the aid of a sharp modelling knife or a special hot-wire cutter. It is often advisable to provide further protection in the form of several layers of acid-free tissue between the object and the Plastazote support.

Bubble-Wrap

The increasingly familiar bubble-wrap is a protective cushioning material made from low-density polyethylene. The wrap comes on rolls of several widths and is available in various bubble sizes, though the 9mm size is probably most useful for packing purposes. Do not use bubble-wrap on objects with a fragile surface unless these have been protected with several layers of acid-free tissue.

It may be appropriate to specify a fire-retardant type of bubble-wrap in certain circumstances.

Environmental and Handing Protection

Cotton gloves

Bare hands, however 'clean', can deposit skin oils, salts and acids on the surface of objects. Cotton gloves offer a simple and cost-effective remedy for the safe handling of slides, negatives, documents and most other types of objects. Plain gloves are suitable for general use but are prone to slip on porcelain and other objects with hard, smooth surfaces. Where slipping is a problem, use cotton gloves with special rubber 'pimples' on the contact surfaces to give an improved grip.

Silica Gel

Silica gel is a porous form of amorphous silica that acts as a dessicant. It is used to control humidity levels in storage containers and display cases. Sachets of the gel are now a familiar packaging component for new electronic, photographic and computing goods. Standard silica gel is normally sold as white granules, but there is a blue self-indicating variety that turns from blue to pink when it has absorbed so much moisture that it is no longer active. Both types can be regenerated by oven heating to 105-120°C.

Buy the gel loose, or choose from a range of standard sized sachets. It is most effective in creating a dry atmosphere in well-sealed display cases or in sealable boxes such as polythene food storgae containers. Art-Sorb is a highly efficient form of silica gel that is available as beads or sheet, and in two sizes of sealed cassette suitable tom control volumes of 0.7 and 1.0 cubic metres.

Tarnish Inhibitors

Freshly polished silver has a highly reactive surface that almost immediately begins to tarnish unless the process can be slowed down. Tarnish inhibiting capsules and tablets protect polished silver for up to 12 months, and are available in various sizes to protect enclosure volumes of up to a cubic metre. Carosil is a widely available brand. Another approach uses impregnated plastics, papers and cloths that absorb tarnish forming chemicals; wrap or fold these around polished metals such as coins, medals and silverware.

Microcrystalline Wax

Many surfaces benefit from the protection of a near-invisible coating of a special microcrystalline wax such as Renaissance Wax - not to be confused with beeswax and similar polishes designed for wood. Newly cleaned or polished metals, or those prone to oxidation or further corrosion, can retain much of their finish without chemical treatment or lacquer coatings. Apply the wax sparingly but thoroughly, and immediately polish it off with a soft cloth, using cotton buds to remove any excess from crevices and detail. The wax is soluble in white spirit, so subsequent applications (after a year say) tend to dissolve the underlying coat and create a new layer --but beware of polish build-up.

Ultraviolet Protection

Ultraviolet light damages textiles, paintings, prints and photographs, resulting in fading, discoloration and embrittlement. Daylight contains a significant ultraviolet component and several types of electric lighting also emit significant levels. Sensitive objects therefore need protection unless they are stored in light-proof containers.

The normal methods of protection involve filtration at the light source or its point of entry. Apply ultraviolet absorbing sheet, film or varnish to windows, skylights and protective glazing; these filters are cyrstal clear, and are available as thin Perspex sheet or polyester film with a self-adhesive coating. The ultraviolet absorption of films and varnishes fades with time, so monitor their effectiveness after 3-5 years. Filters are also available for fluorescent lamp arrays - which emit relatively high ultraviolet levels - and as sleeves for individual tubes.

Cleaning Materials

Cleaning is a process that is both essential and a potential threat to the long-term stability of objects. This apparent paradox is avoided if museums contain their routine cleaning to the removal of dust from objects, stores and display areas; the avoidance of wet and solvent cleaning wherever possible; and the referral of any cleaning problems to a conservator. Effective storage methods using many of the materials described above reduce the frequency and severity of cleaning activity.

The core of the cleaning armoury should consist of good vacuum cleaners, various types of brushes, and muslin or other suitable filters for vacuum cleaner nozzles. Brushes can be obtained from artists' shops and the suppliers listed at the end of this sheet. Vacuum cleaners now come in a wider range of options, even at the domestic scale. Newer cyclone-based types and their rivals offer more effective cleaning, and better filtration of the exhaust air using a variety of mechanical, active and electrostatic filters. In the domestic environment these filters may be overlooked, but in the museum it makes sense to clean or replace them at the manufacturers' recommended intervals. Investigate the availability of spare parts such as bags, belts and filters when ordering or buying a cleaner.

The museum's need for other cleaning materials will depend on the advisability of undertaking the work in-house and the expertise of individual staff. Materils that may find a place in most museums include deionised water, special detergents, industrial methylated spirit, and specialist metal cleaners such as Peek or Goddard's Silver Dip. Read catalogues and lables carefully to make sure that the materils are genuine and not merely domestic products masquerading under plausible descriptions.

Pest Control Materials

Pests such as the common clothes moth and furniture beetle were once very common, but modern cleaning methods and materials together with more efficient heating and ventilation have dramatically reduced their threat. At the same time, environmental and health and safety concerns have brought about a reappraisal of pest control techniques. There are now far fewer commercially available products for dealing with pests.

The trend now is towards integrated pest management (IPM), which concentrates on regular monitoring for pest activity, the maintenance of an environment that discourages pests, and sensible storage using conservation materials. Where treatment is necessary, it is specifically targeted rather than indiscriminate, and increasingly relies on non-chemical methods - for example, by subjecting objects to low temperatures or carbon dioxide or nitrogen atmospheres.

In other words, do not be tempted to rush out and buy chemicals. Instead, ask a conservator to help your museum develop an integrated approach. For more information about pest control see:

Pinniger, D. and Winsor, P. Integrated Pest Management, Museums and Galleries Commission, London, 1998.

Suppliers

The companies listed below sell their products mainly to museums and conservation practices. Many of the titems they stock have very specialised applications and should only be used by trained conservators. However, they also sell the basic collection care products described above in quantities suitable for small museums, archives and libraries.

The suppliers' catalogues contain much useful information, but if you are in doubt then contact a conservator for guidance.

Atlantis European
7-9 Plumbers Row
LONDON E1 6RU
Tel: 020 7377 8855
Fax: 020 7377 8850

Conservation by Design Ltd
Timecare Works
5 Singer Way
Woburn Industrial Estate
Kempston
BEDFORD MK42 7AW
Tel: 01234 853 555
Fax: 01234 853 334
Email: info@conservation-by-design.co.uk
http://www.conservation-by-design.co.uk

Conservation Resources UK Ltd
Units 1, 2 and 4
Pony Road
Horspath Industrial Estate
Cowley
OXFORD OX4 2RD
Tel: 01865 747 755
Fax: 01865 747 035
Email: 100436.34467@compuserve.com


Preservation Equipment Ltd
Vinces Road
Diss
Norfolk IP22 4HQ
Tel: 01379 647 400
Fax: 01379 650 582
http://www.preservationequipment.com

Secol Ltd
15 Howlett Way
Fison Industrial Estate
Thetford
Norfolk IP24 1HZ
Tel: 01842 752 341
Fax: 01842 762 159

Charcoal Cloth International
High Tech House
Commerce Way
Arena Business Park
Houghton-le-Spring
Tyne and Wear DH2 5PP

For more information on suppliers, please refer to the Museums Yearbook Buyer's Guide to Suppliers and Services. An online suppliers guide is also available at: http://www.musuemsassociation.org

The Society of Archivists also publishes a Directory of Suppliers, available from http://www.archives.org.uk

The inclusion of a supplier within this fact sheet does not imply the approval or endorsement by MLA of the product or service. You are therefore urged, in your own interests, to ensure that any product or service is appropriate to your needs.

For more information about private conservation work please contact:

Conservation Register
Tel: 020 7721 8246

Conservation Register (Scotland)
Tel: 0131 668 8668

Copies of this fact sheet can be provided in alternative formats. Please contact Viola Lewis, Information Officer at MLA for further information.

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