Government of Canada, Canadian Conservation Institute. They can also be used for the base of display cases where the interior surface of the panels is not visible to visitors. This section provides advice about choosing the right product from the wide range available and about avoiding situations that present significant risks of damage to objects. A polyurethane gasket is another example of a product with a limited lifespan of about 1020 years, changing from rubbery to brittle (as shown in Figure 3) and thus losing its gasketing ability. Waxy residues have been found on the skin of polyethylene foam planks, probably acting as a releasing agent, observable under optical magnification deep in the creases of the skins film. Note the loose beads from the expanded board. Small enclosures such as containers are extremely useful for storing museum objects because they can provide very good protection against physical forces and, depending on how they are made, can also protect against external agents such as pests, pollutants and large RH fluctuations in the room. However, foam boards with a laminate made of acidic paper, thin cardboard or wood veneer, or PVC rigid board may need evaluation to ensure their compatibility with the objects that they may be in contactwith. Even with recommended coatings, there is an important factor to consider: the drying period. Risk management knowledge helps decision makers understand that they have some flexibility in selecting products for their specific contexts and needs. To determine if a fabric, paper or matboard (whether wet or dry) could transfer dye to objects. many types of Tupperware containers, Lock & Lock food containers) and poly(ethylene terephthalate) (PET) are the most commonly used materials for small clear plastic boxes. In museums, they can be used to support large-sized flat objects. Can use a positive-pressure filter system. Small and flexible tubes are mainly used as padding and interleaf over monofilament thread or metal rod mounts. Synthetic and natural rubbers will lose their initial chemical and physical properties after a few decades. Figure 33. Coloured translucent and opaque acrylic and polycarbonate sheets are available, as well as those with a mirrored look. CCI 120279-0005Figure 6. Interleaving (e.g. Figure 26. Fortunately, for many applications, products do not need to be chemically and physically perfect, such as when the objects are non-reactive (or slightly reactive) or robust or are not located close to emissive products. Government of Canada, Canadian Conservation Institute. Avoid direct contact of PVC with an object and avoid using it in an airtight enclosure for more than 10 years. Although polycarbonate panels have better impact resistance, acrylic panels remain a more popular choice for glazing. Internal padding was provided, then the boots were secured to foam blocks with cotton twill tape and padded out with crumbled acid-free non-buffered tissue paper. Common silicone sealants are often of the acetoxy type. The main source of hydrogen sulfide in collections remains visitors and external sources. Government of Canada, Canadian Conservation Institute. They can be made of different materials: Consult CCI Note 13/3 Rolled Storage for Textiles for more details. The corrugated sheets are available in different thicknesses and many colours. It is also wise to avoid stacking many boxes on top of each other, as shown in Figure 17. For example, if the box is placed near cold walls, it is at high risk of becoming cool and damp inside. Government of Canada, Canadian Conservation Institute. Ensure proper air circulation between objects and moisture and pollutant sorbents. CCI 100426-0013
Government of Canada, Canadian Conservation Institute. Compared to glass, acrylic panels are more resistant to impacts and significantly lighter. Consult also Plastic boards and panels for details on plastic materials used for display purposes. damage that occurs to objects by airborne pollutants emitted by products (Table1); damage that occurs to objects by direct contact with products (Table 2); and. Consult. With archival documents, all sticky notes (e.g. Those made of a thin layer of polystyrene adhered to the foam core can be used safely in terms of minimal risk of off-gassing. Honeycomb panels are a very light and versatile alternative to other kinds of heavy sheet products such as wood panels. A semi-transparent paper called glassine is sometimes used as an envelope to store negatives and photographs. Place the weight above the stacked assembly to compress it for good contact. Some of these materials also contain sulfur compounds. Government of Canada, Canadian Conservation Institute. Note that some honeycomb panels are finished with potentially problematic materials such as acidic paper, cardboard or wood veneer. Government of Canada, Canadian Conservation Institute. Diagram showing how to assemble the materials and sample to carry out a colourfast dye test. It may even be good to have fire-resistant containers, although the products used to make them should not be impregnated by flame retardants since not all of the compounds that make up flame retardants are safe for objects and some could cause alterations to objects in a closed environment. This section describes the principles that guide the selection of products typically used for display, storage and transportation. Matboard made from highly purified wood pulp buffered to pH 8.5 is an acceptable, more economical alternative. High-pressure laminates are good vapour barriers and are available in different colours or patterns. to make display case bases. Typically avoid stacking more than three boxes, and use shelving with sufficient shelves to store the objects both safely and in a compact, space-saving manner (Figure 18). Ttreault, J. Some hard foam boards are made of rigid PVC foams. Ventilation inside a leaky enclosure occurs by stack pressure, which allows dust infiltration. The vase is on a pedestal base that releases harmful compounds, some of which migrate into the object at the contact point (left). Coloured paint, especially dark colours, will need a longer drying period (Figure 4). As well, it is recommended that two types of photographs be stored in neutral pH papers because they are potentially sensitive to high pH. pp. [consult Table 3]). low-cost common urethane foam (ether or ester type due to their short lifetime issues [consult Table 1 and Table 2]), soft PVC foam (it can degrade faster than rigid PVC). For example, numerous types of plastic sheets or panels are expected to embrittle or weaken to such an extent that within 30 to 50 years they are liable to tear or crack under stress. External sources may help you find information on other products, as well as further information on products covered here. Figure 18. The trade name Saran Wrap used to be the most common stretch wrap on the market, and it was originally made of PVDC. The rust that developed on the iron will then stain the copper object. single or double corrugated layer). PolyPlank is a similar product, offering similar density and sizes. The same applies for all staples and paperclips (Figure 1). He has given more than 100 seminars in Canada and Western Europe on preventive conservation issues such as lighting, environmental guidelines, and exhibit and storage materials. Manufacturers do change the formulation and manufacturing processes of products over time, usually for the best. A wide variety of fastening devices and techniques can be used to connect the walls together to make the box. CCI 120171-0012, Government of Canada, Canadian Conservation Institute. For polyethylene (PE) foam board and polystyrene (PS) insulation foam board, consult Foam planks, thick (>13 mm or 1/2 in.). Most rubber-like tubing could contain harmful products (sulfur or plasticizer or both), while most low-cost heat-shrink tubing sold in electronic shops are made of PVC and contain plasticizer. Figure 14. For long-term use of foams, such as for object storage mounts, it is best to use only new foam. Provides weak protection (depends on the design). Rods are defined as filled rigid cylinders. or immovable (such as architectural interiors, monuments and historic buildings). A low-odour or neutral cure silicone (based on oxime or alkoxy), such as GE Silicone II, is a much better alternative as a sealant. Contact between metallic objects and metallic products may cause galvanic corrosion in a highly humid environment (described under Contact). Department of Canadian Heritage
The introduction of an interleaf will block the migration (middle) but not the off-gassing (right). One way to avoid dealing with the prolonged airing-out period needed when using wet coatings is to use wooden panels already covered by a stable vapour barrier or laminate, or to apply a laminating film on the wood product that will seal in any off-gassing emissions. The air cells can be as small as 6 mm (1/4 in.) Figure 41. The interleaf must have good gas-barrier properties and be free of compounds that could be transferred through contact. Post-it) should be removed from direct contact but kept and preserved properly. Tyvek in general is further described under Fabrics. Polyethylene (PE) foam sheets, such as Cellu-Cushion, are available by the roll with a thickness ranging from 1.6 to 6 mm (1/16 to 1/4 in.) Example of a storage mount carved out of polyethylene foam and lined with fabric. Over time, adhesive on an object can become brittle or viscous, suffer bond failure and cause staining (Figure 6) that can be difficult to remove. CCI 125773-0010
Support for archaeological objects made of crosslinked polyethylene foam. Due to its great stability, this plastic is often recognized as an archival product. be stable under light (a criterion for a long-term exhibition). For information on UV filters, consult CCI Note 2/1 Ultraviolet Filters. Acidic matboards are known to damage paper artwork, as shown in Figure 11. In conservation, the water-impermeable Tyvek 1443R grade is often recommended, but breathable (punctured with tiny air holes) varieties are also made. Plastics are synthetic compounds made of long molecular chains called polymers. However, plastic panels allow slow permeation of oxygen and water vapour, and very large variations in RH can affect the dimensional stability of plastic sheets. (TVOC: total volatile organic compounds). Understanding the nature of both the objects and the products that will occupy the same environment is important when assessing the risk of any potential interaction between them. Consult the section on Containers to see how corrugated sheets are used to make boxes. Avoid using recycled foams since they may contain polyethylene that is already degraded, and this can affect the lifetime of the new recycled foam. as a first layer of shock-absorbent material), to fill up the extra space inside a hard container such as a shipping crate or to bulk out the inside of objects with a soft cushioning material generally added to more fully pad and protect areas of the object that are in contact with the container (example in Figures 20 and 21). If any doubt arises regarding the safety of the removal process, a conservator should be consulted. Open-cell foams are recommended in situations where the foam will be compressed often or will be under steady, heavy pressure. Wood products or wood-based boards are composites made chiefly of wood and glue. 1030 Innes Road
2002). Some materials have a limited lifetime. Only when wool is almost touching sensitive metals, such as silver, is there a cause for concern. In closed-cell foams, each cell is completely enclosed by a thin wall of plastic; in open-cell foams, the individual cells are interconnected. Glazing for display cases or frames can be made of glass or clear rigid plastic panels. the environment to which the product is exposed (e.g. Melinex 516 (formerly called Mylar type D), Hostaphan 43SM and Terphane 10.10 are transparent PET films that are recommended because of their high-stability and low-additive content. They are commonly used in conservation as flat bases or platforms or to make backing boards, folders, trays (Figure 9) and boxes. CCI 120171-0015
Mylar D used to be recommended for long-term archival use, but it is no longer produced. Recesses were carved out of the foam, and a base was made out of a second sheet of foam plus an outer sheet of corrugated plastic board. Weak acids, such as formic and acetic acids, will penetrate the paper layers easily. Cellulose acetate sheets fall into this category as they suffer accelerating deterioration due to acid hydrolysis and release acetic acid. Low-cost polyurethane foam, often used as cushioning in transport packing crates, is also problematic at the end of its life cycle. Although it is not conclusively proven that buffered boards can slow down the degradation of papers, at least they will not further contribute to their degradation. As for the resin-impregnated paper types, the most common products are acidic but some made for the museum and archival field are acid-free. Because most products are not designed for the preservation of museum collections, their use in some cases can lead to unintended damage. CCI 88702-0154
CCI 123327-0008
Unfortunately, from time to time, the change may affect properties that are a concern for museums; for example, the adhesive is more acidic or the lifetime of a product is shorter. Figure 35. This context can be identified by three main parameters: Table 4 summarizes the risks of pollutant damage on collections stored in different contexts: with the product and object in contact or not, and in different enclosure designs (in an enclosed, either partially or fully airtight space, or in an open space, such as a room). Government of Canada, Canadian Conservation Institute. In sheet form, PVDC may contain up to 10% plasticizer. airtight (protection against external pollutants and insects and to some degree against large RH fluctuations); waterproof (if not stored in a waterproof cabinet or not covered by a plastic sheet); strong enough to support the weight of objects they contain when lifted, plus other possible loads (such as the weight of one or two other boxes potentially placed on top); labelled to allow ease of identification during retrieval; and. An electrochemical cell is created where the metals act as anodes and cathodes in the presence of an electrolyte (water with salt). The plastic on the other side of the foil is nylon, which has a higher melting point. For example, plywood is a product made of two materials (wood and adhesive) and can be used as is as a platform or can be assembled with other products to make display cases or packing crates. More details about the selection and use of coatings can be found under Coatings, laminates and films. Government of Canada, Canadian Conservation Institute. A twined basket with a silk lining, stored within a custom-made box constructed of acid-free corrugated paperboard. Another option is plastic-laminated aluminum film, such as Marvelseal 360. CCI 120171-0014
Government of Canada, Canadian Conservation Institute. Known as Plexiglas, Perspex, ACRYLITE or simply acrylic, this transparent sheet is popular for making display mounts (Figure 8) as well as cases (consult Glazing and glazing films for more information on display cases). If testing a product: place at least 2 g of the product in a glass jar with two or three previously wetted pH strips, and seal the jar. Lavdrine, B. In indoor environments, many metals tend to slowly tarnish and may stain objects that they are in contact with. For example, if a large copper object is in contact with an iron wire, the wire will corrode at the contact point when exposed to high humidity since iron is less noble than copper. They may be used when assembling airtight display cases and containers. Government of Canada, Canadian Conservation Institute. CCI 120078-0223. These products should be selected and treated in the same manner as for Fabrics, described above. After four weeks of off-gassing, the curves flatten off, so there is not much to be gained by airing out the painted surfaces further. migrating from the product to the objects surface at the point of contact, Whitish or pale-coloured objects, porous objects: stain is more visible and disfiguring, Compounds from degraded polyurethane foam, Unsealed or poorly sealed wood products (knots can stain even more), Some dyed fabrics, paper and matboards (non-colourfast dyes may run if exposed to water or high RH), Oil stain, leaving an appearance of a wet or a dark spot, Porous objects: stain will penetrate and be more difficult to remove, Silicone oil from some silicone foams, gaskets, tubes and sticky waxes or gels (such as museum gel), Lubricants from a mechanical system of drawers, doors on cabinets or any other enclosure, Objects surface physically damaged (delamination, losses) when object and product stuck to it are handled and incautiously unstuck, Object disfigured because product residues remain stuck on surface, Objects with a bonded (laminated, layered, painted, coated, adhered) or fragile surface are more at risk, especially if bond is weak, Glycols from opened paints after a few weeks or from opened coloured or dark paints after many months, Degraded flexible PVC (including synthetic leather [leatherette]), Leaching of compounds from objects surface due to exudate on products surface, Photographic transparencies: losses in dyes and image, Viscous plasticizer exudate on degraded flexible PVC, Corrosion products from copper staining the label glued on it, Salt contamination and efflorescence (damage is highly influenced by high RH), Various porous objects (such as brick and marble): spalling and losses to surfaces, disfigurement, Salts present in contaminated products (e.g. For simplicity, only a few products that were known to be safe for this purpose were used: Not all products were reviewed in this Technical Bulletin. Fabrics, including jersey knits, plain weaves, felts and velvets, as well as non-woven materials such as Tyvek, are commonly used as finishing materials, providing an aesthetically pleasing soft covering layer or interleaf and in some cases providing a certain amount of padding. not contain sulfur-based compounds (consult. The guidelines will not necessarily provide complete protection in all situations or protection against every adverse effect possibly caused by the use of products in museum contexts. The author welcomes comments. Figure 43. For storing photographic documents, archival institutions commonly select envelopes or sleeves that pass a test called the photographic activity test (ISO 14523:1999, Ttreault 1999). Foam boards are light and somewhat fragile. If using coloured matboard, ensure that the dye is fast (consult Test #3: Testing for colourfastness). 1725. Objects can be composed of one or more materials and can be movable (such as archaeological and historic artifacts, paintings, books, archival documents, furniture, costumes, etc.) Another LDPE that is becoming more common is the linear low-density polyethylene (LLDPE), also called stretch wrap. This PE probably has a limited lifetime, especially when stretched, and provides low gas barrier protection. Cotton twill tape was used to secure it to the carved, recessed and padded polyethylene foam within its transportation crate. Government of Canada, Canadian Conservation Institute. Extruded plank polystyrene boards (above) and expanded bead (below). The best practice recommends the use of buffered (acid-free) wood pulp-based products including paperboards for the storage and display of photographs and paper documents. In this context, the term product describes a manufactured or processed substance composed of one or many materials, which can be used alone or assembled with other products into more complex finished items. PET film also has a very low permeability coefficient to hydrogen sulfide (Ttreault 2003 p. 135) and thus, if made into a tightly sealable bag, it can be useful to store silver, possibly in combination with a sorbent such as Pacific Silvercloth. Wait 24 hours. In the archival field, Tyvek envelopes are used to store archival documents, photographic negatives or other small items. Figure 44. However, most uncoated metals will tarnish slowly with oxygen and water vapour in the environment and can eventually stain objects through contact (Figure 1). Further tests for detecting harmful compounds in products used in preventive conservation can be found in the following publications: To determine the presence of sulfur. It is stored on a plank of PE foam, padded with a layer of polyester quilt batting and lined with Tyvek. Detail of two PVC slide holders showing stains and warping, signs of their physical and chemical deterioration over time. Government of Canada, Canadian Conservation Institute. Some polycarbonates are slightly less crystal clear than acrylic. They take months or a few years to degrade when buried in an anaerobic landfill. For both powder-coated and anodized metals, no drying time is needed. For this reason, the use of coated metallic units is recommended if contact with objects is expected in both the short and long term. Ottawa, ON: Canadian Conservation Institute, 1999. The product may provide an inadequate contact surface, such as one that is narrow or sharp (resulting in unequal pressure points) or that is abrasive or too hard. Disclaimer: The information provided in this Bulletin is based on the current understanding of the issues presented. Since 1998, he has also been a board member of the Indoor Air Pollution Working Group, which holds conferences every two years. Table 5 describes in more detail how enclosures at three different levels of airtightness affect objects exposed to pollutants or to other agents of deterioration. For a more complete formula, one needs to consider extra parameters such as the concentration of pollutants outside the enclosure and the capacity of other products to sorb pollutants. Figure 46. Many types of silicone sealant are available on the market; they come in clear or coloured varieties and some can be painted. A gasket is usually made from a material that yields so that it is able to deform and tightly fill the space it is designed for, including any slight irregularities. 145152. Metals such as steel plates might also be considered ideal products because of their durability and their absence of off-gassing. Polyethylene foam planks can be easily glued together with hot-melt glue or welded with a hot air gun, if greater thicknesses are needed (Figures 27a and 27b). Fortunately, with new volatile organic compound (VOC) regulations in Canada and the UnitedStates, these coatings are becoming less and less available. (In contrast, cell cast acrylic is recommended for framing and display cases because of its superior optical clarity.) In general, when ambient RH is well-controlled, adequately coated wood and wood products should be acceptable for enclosing most objects, except those containing lead. CCI 120171-0017
In practice, it is best to use transparent wire and tubing to minimize visual interference. Figures 10a and 10b. Government of Canada, Canadian Conservation Institute. No accelerated methods were used. In addition, there is sometimes a third phase in which rapid degradation after a period of time causes significant emissions. Adhesives used in an open space do not present a significant off-gassing problem. Commonly known simply as PVC, this plastic is usually supplied in the form of flexible sheets or tubing. Extruded polystyrene (XPS) foam also comes in the form of various agglomerates that can serve to bulk out a package. A variety of sleeves and envelopes are commercially available. Some large panels made of polycarbonate (such as Verolite) and acrylic are available and are used for building structures (twinwall or multiwall) such as greenhouses. Wrapping a rolled textile with two to three layers of acid-free or alkaline-buffered tissue paper provides an effective, low-cost barrier against dust and reactive outdoor pollutants, such as ozone and nitrogen dioxide. Recycled corrugated sheets should also be used for short and medium terms only because a portion of the polymer has probably been partly broken down and oxidized in its previous life. Unfortunately, this type of silicone releases a substantial amount of acetic acid during curing (easily recognized by its vinegar smell) and should not be used inside enclosures. The reverse can also happen where solid compounds from the product can become stuck to the object, as shown in Figure 4. Note that acrylic panels are easily scratched unless scratch-resistant products are used. Photographs of the Past: Process and Preservation. The coatings that are generally acceptable in archival and museum contexts are acrylic or acrylic-urethane emulsion paints (latex) and, for special applications, two-part epoxy and two-part urethane paints. Little protection from risk of infestation. Government of Canada, Canadian Conservation Institute. Sheets of acid-free buffered or unbuffered paper are useful as a light covering material over objects, as thin interleaves or as a wrapping layer. Rigid PVC foam boards are not recommended for use in contact with objects or in a fairly airtight enclosure for long-term purposes. An accelerated corrosion test called the Oddy test (Green and Thickett 1995) is often used to detect the presence of volatile acids and other gaseous compounds that can harm metals and other sensitive materials. A balance between optimum preservation and visitor access must be considered. Determine the products chemical composition and its formation process. Polypropylene foam, known as PropaFoam or PolyPro, has similar properties to polyethylene foam with the potential for a longer lifetime. The boxes are made of polypropylene and polyethylene or both as a copolymer. This flexibility can be useful for assigning priorities when resources are limited. Also, some wood products, such as medium density fibreboard, can be made of post-consumer recycled content which is good from a sustainability point of view. As well, UV radiation which damages many types of objects can be filtered at the level of the glazing layer when display cases or glazed framing are used. Anti-reflective products that help reduce glare caused by spotlights or room lighting are also options. Entitled Commencement of the Action Between His Majestys Ship Shannon and the United States Frigate Chesapeake, this work of art belongs to the Art Gallery of Nova Scotia, accession number 2003.397. In the first years of the 21st century, about 275,000 objects from two museums were moved to the new Muse du Quai Branly in Paris. Some polypropylene sheets are made to be biodegradable. These rubbers can stain other objects through contact or by off-gassing in enclosures. Physical damage can occur at contact points between the object and the product. CCI 120171-0009
Exposure to high concentrations of volatile compounds may not result in visible damages or mechanical changes in objects in the short term but can initiate chemical alterations that could affect them in the future. Their core being plywood panels, these products can be cut and assembled easily and are quite sturdy. If compounds such as sulfur dioxide (SO2), sulfur oxides (SOX), sulfuric acid (H2SO4), hydrogen sulfide (H2S) and carbonyl sulfide (COS) are listed, the presence of sulfur is confirmed and the test is no longer needed. These papers are alkaline and more permanent than unbuffered papers. Corrugated boards are available in a few different thicknesses (e.g. CCI 124883-0019
Otherwise, the use of an interleaf between the bubble wrap and the object is recommended to avoid potential staining. Raise enclosures 10 cm (4 in.) not associated with any specific distributors or manufacturers) are free and particularly recommended: The following are recommended as useful references that provide information on products and on strategies to use them safely with objects: Barclay, R.L., A. Bergeron and C. Dignard. (Do not use these products inside an enclosure without making a proper risk assessment. Composite laminated panels with rigid metal skins on rigid or foam plastic cores, such as the aluminum composite products made by Dibond, Reynobond or Alucobond, are being successfully used to provide a metallic look when building display cases. Glycerol (glycerine), which is available at drugstores, Glass jar with screw-top lid (250 mL or smaller) for testing a product, Absorbent material, such as blotting paper or a piece of prewashed white cotton cloth, approximately of the same size as the plates mentioned above, A 1 kg weight (approximate), for example a book or a block of metal.