Caring for basketry and plant materials

Bark

Bark describes the outer layers of stems, branches and roots of woody plants. The outermost tissue of a tree is composed mostly of dead tissues called “cork cells” that contain suberin, a fatty and waxy substance that makes the outer bark more resistant to water and microbial action.

Bark also contains lenticels that function as pores on the living tree and allow the exchange of gases. They can appear as light or dark lines or spots and can be used as an identification aid (Figure 1).

Birchbark (bark from Betula papyrifera, known as white, paper or canoe birch) is commonly used by several Indigenous communities in Canada to make objects such as open containers, boxes, cradles, scrolls with pictograms, decorative ornaments (bark biting) as well as covers for shelters and canoe frames. Birchbark is collected in the winter or summer, but the winter bark is usually sturdier and thicker and is also darker coloured, usually orange-red to dark brown. The dark layer can be partially removed to create decorative designs (Figure 2). The bark is easier to remove in early summer when the sap is flowing, but if peeled from the tree in hot weather, the bark can separate into thin layers (Adney and Chapelle). Prior to use, the bark is usually submerged in water to make it more pliable and therefore easier to shape. Birchbark is naturally resistant to decay and is waterproof. Well-stitched and caulked birchbark can be made into containers that hold water or into leak-free canoes that float on water (Figure 3).

Some barks are fibrous, such as what is commonly called “cedar bark” (Figure 4), which is inner bark of the western red-cedar (Thuja plicata) or the yellow cedar (Cupressus nootkatensis). On a living tree, the outermost layers of inner bark cells die progressively, forming a protective layer. As cells behind the protective layer die and the diameter of the tree trunk increases, the outermost layer shreds off. When traditionally harvested for use, a long strip of bark is pulled off the tree, the rough outer surface is removed and the inner bark is dried. Strips are woven or otherwise interworked to create baskets, mats, hats, garments (Figures 5a and 5b) and cordage. They are also used as strands attached to objects such as Northwest Coast masks.

Root

Root is used as a lashing and binding material and can be woven into intricate objects (Figure 6). Spruce root in particular is often used by Indigenous peoples of Canada; western red-cedar, pine and other tree roots are also used. Roots have the same basic cells as those found in the tree stem, but the cell walls are thinner and the tissue is more porous. Young and tough roots from mature spruce trees are excavated in the spring, when the bark is easier to remove. Soon after collecting the root, its bark is removed, exposing a smooth surface with a satin lustre. Roots are split and then dried to prevent the growth of mould on them. Prior to use, the root is soaked in water until it becomes flexible.

Wood splint

Varieties of young hardwoods (e.g. maple, ash, white oak) are split to produce thin, flat and flexible splints that are used to make various objects. One method is to cut a log and beat it until strips can be removed along the growth rings. The strips can be thinned and smoothed, made to the desired width and then used to create the object (Figure 7).

Leaves, stems and grasses

Many types of grasses, leaves and stems have been used to make or decorate baskets (Figure 8), hats, handbags, mats and other objects, as well as to make cordage. Some grasses and stems may be delicate, such as the maidenhair fern stem primarily used as a decorative element, or very strong and rigid, such as bamboo or rattan. Grasses characteristically have no, or very little, xylem (woody tissues) and have hollow stem interiors. Many have a long thin structure and can be easily worked, but they tend not to be as durable as woody tissues. The grasses are collected at the desired size and, depending on the type of plant, they may receive some treatment prior to their careful drying. Drying in the shade preserves their colour, while drying with some sun exposure will bleach and lighten colours.

Long strong leaves or husks (Figure 9) can also be used, such as leaves of corn, palm and raffia.

Cane

Cane usually refers to strips of the outer, shiny skin of rattan, a term used to describe several climbing palms of tropical Asia that have long, tough, slender stems. Cane is used to make chair seats or backs in a weaving pattern known as caning. “Cane” and “reed” are commonly used terms to refer to various grasses and reed species with a long, thin stem, many of which are used in basketry.

Wicker

Wicker is used to describe the stems or slender branches, either whole or split, of more than twenty types of immature willow. It is used to make relatively sturdy interworked objects (baskets, furniture, etc.) and is associated with a distinct weaving style called wicker or wickerwork. Wicker is also used as a more generic term to describe any whole or split basketry element that is sturdy, made from other plant species.

Dyes

Some plant parts can be readily dyed, but other parts may not allow good penetration of the dye. Barks, flowers and other plant parts have been used to colour plant materials for woven objects, although in the recent past, craftspeople and artists have turned to synthetic dyes.

An ancient dyeing technique to attain dark-coloured organic materials was to soak the material in a tannin-rich bath of barks and twigs, followed by soaking in an iron-rich solution such as water in an iron pot or with iron shavings or nails added, or immersion in iron-rich mud. Chemically, the iron acts as a mordant in the dyeing process and binds to the plant material. Depending on the barks and twigs used in the initial bath, the resulting materials may be black or very dark tones of brown, sometimes with a hint of olive green. But iron also has the ability to act as a catalyst for some chemical reactions; notably, it can catalyze cellulose degradation mechanisms. Thus, such black-dyed plant materials are particularly prone to damage and losses, because the iron bound to the fibres actively causes their degradation (Figures 10a and 10b). When a material deteriorates at a significantly accelerated rate due to internal compounds used in its manufacture, it is sometimes described as suffering from an inherent vice.

Coiling

A foundation material (one or several rods, or bundles of smaller plant materials) is coiled to create the shape of the object, and the coils are secured in place with stitches. Some foundations may be pierced through, or the stitches can bind one coil to another by using several connecting techniques. The stitching materials are the active materials, so they are usually more flexible than the passive foundation materials. Stitches can create decorative patterns (Figure 10a), as does varying the size of the foundation and the spacing of the coils.

For decorative purposes, different stitching materials and techniques can be used to create patterns, or a different material can be laid against the foundation and held in place with stitches. A technique called “imbrication” (overlap) is also used, where a strip of a decorative material is applied to the exterior side along a coil row. The strip is interlocked into the structure by inserting a fold under a stitch element; then, the stitch is pulled tight to wedge it securely in place. The strip is brought back over the stitch, where it is folded again and held in place by wedging it under the next stitch element (Figure 11a). The application continues so as to create the desired design (Figure 11b). Decorative patterns can be produced by having the overlay hidden along the coil behind several stitch elements for a certain length and then having it reappear further along by bringing it forward above the stitch element.

Twining

In twined basket construction, the vertical elements (stakes or warps) are passive and the horizontal elements (weavers or wefts) are active. Usually, two weft elements are used together—one element comes to the front of the work as the other goes to the back, and they go over and under each other to produce an intertwining. If the same warps are used for each row, it is identified as simple or plain twining; if the engaged warps are offset, a diagonal (twill) effect will be created. Wrapped twining involves the use of elements perpendicular to one another, held together with a flexible twining element. Figures 12a and 12b show how, row by row, flexible wefts secure together the areas where the two other stiff strands meet. Some twined basketry has warps that cross each other diagonally; the weft is worked in along the rows where the warps cross.

Figures 12a and 12b. The crab trap (left) is made with two stiff elements held together with the wrapping of a more flexible material (right). This object belongs to the Museum of Anthropology at the University of British Columbia (accession number: A2191).

False embroidery is used in plain twining as a method of structural decoration. A decorative material (e.g. grass stems, porcupine quills) is wound around the exterior weft so that the design shows only on the exterior side. The decorative material slants in the opposite direction to the weft (Figure 13). Designs can also be made with a material that overlays the weft, and if a half twist is made as it passes behind the warp, the pattern can be seen on the exterior and interior surfaces (Figure 14).

Plaiting

In plaited basketry, there are no distinct warp and weft elements: all elements are active and are often of the same size. Simple (checkerwork) plaiting is over-one, under-one in both directions; diagonal (twill) patterns can also be created.

Wickerwork

Wickerwork consists of strong interworked constructions suitable for using strands of wicker (slender branches of willow) to create objects such as sturdy baskets and furniture. Wicker is the traditional material of choice for these types of constructions, but other strong materials such as cane can be similarly used. Because the materials are more rigid, both horizontal and vertical elements may move within the structure. The wefts do not cross other wefts in a given row.

Splintwork

Wooden splints of various width are woven, usually using plaiting techniques. Additional thin strips can be added to the weft and twisted to create a decorative structure that projects out from the basket (Figure 15). The rim of the basket may also be reinforced with a separate hoop, possibly of carved wood, that is lashed to it.

Sheets of bark

Birchbark can be used as a single piece, cut or folded to create the desired shape and then stitched together (Figure 16). The bark sheet side that originally was facing the tree trunk is usually placed to face the exterior side of the object. The bark can also be cut in strips and plaited. Birchbark can be the foundation for quill decoration (Figures 16 and 17).

Recommendations

• Provide enough space on shelving units for each object. This makes it easier to find an object, examine it and handle it. Follow good handling practices. Ensure that nothing will bump into or snag on elements that project out from the surface.
• Pad interiors of flexible baskets to maintain the shape, without overstuffing. Use soft materials that will not snag inner elements—crumpled archival tissue or a set of small polyethylene foam pieces covered with fabric or with a soft polyethylene non-woven sheet (Figures 27a and 27b). One can also insert a bag made of fabric, of polyethylene plastic or of polyethylene non-woven sheet (Tyvek) and gradually pad it out with polyester fibrefill. Ensure that distortions that indicate original use of the object are retained.
• Provide outer support around objects (Figure 27c). Outer supports can be made by cutting a recess for the basket into a block of polyethylene foam and lining it with thin foam, fabric or a non-woven sheet (Tyvek). Such supports are most needed for baskets with a small diameter base but larger diameter walls. Another option is to form rings, for example using fabric or medical stockinette (knit cotton, polyester or a blend) filled with polyester fibrefill, or using polyethylene foam pipe insulation made into a ring by stitching the ends together with twill tape or a dab of hot-melt glue.
• Enclose fragile or delicate objects in archival boxes or in plastic containers (Figures 27c and 27d). If there is more than one object per box, separate the objects with a protective layer of thin foam. On the exterior of the boxes and containers, indicate the objects’ accession numbers and apply images of the objects so that they are not handled unnecessarily.
• Larger or heavier objects such as a bark-covered canoe may need several supports placed at strategic points. Consider the use of carved rigid foam, shaped and padded wood or adjustable slings. (For a description of an adjustable sling, consult R.L. Barclay 1988.)
• Tie loose or broken elements to the object with soft fabric tape. Do not use tapes with adhesive (Figure 28).
• Baskets should not be stacked one inside the other, even if their condition is considered good. Stacking is suitable for flat objects (e.g. mats and tapa sheets) if there is an interleaf of archival tissue or lightweight paper between each object. The bottom object must be able to tolerate the weight load.
• Store flat objects in narrow drawer cabinets or archival boxes. Roll oversized objects on large diameter tubes to reduce the space needed for storage and to facilitate handling and movement. Note that the tubes should first be covered with Mylar or polyethylene sheeting then wrapped with unbuffered acid-free tissue paper or prewashed cotton sheeting. For further information on rolled storage, consult CCI Note 13/3 Rolled Storage for Textiles.

Consult Handling heritage objects for further guidance on safe handling practices for heritage objects and collections.

Recommendations

• Keep basketry and other objects made of plant materials away from water sources, such as water pipes or storage areas below washrooms.
• If objects made of plant materials do become wet, place them on a stiff board or tray and take them to a well-ventilated, drier area. If the structure is misshapen, pad it gently to shape using strips of thin foam, or a plastic bag filled with crumpled tissue paper, fibrefill or loose scraps of foam. After some drying has taken place, empty out and replace the plastic bag with loose crumpled tissue paper for further drying.

For further information on general issues concerning the risk of water damage and on the prevention of that risk, consult Agent of deterioration: water.

Recommendations

• Maintain good storage practices so objects can be easily accessed and seen.
• Design and maintain an integrated pest management (IPM) program.
• Bag and seal the object when insect activity is suspected. Isolate new acquisitions or loans so they can be observed for insect activity prior to integrating them in the collection.
• If insect activity on the object is confirmed, follow through with a method to kill any active insects.

For aids regarding pest identification and strategies to control pest damage, including IPM, consult:

• Agent of deterioration: pests
• MuseumPests.net
• CCI Note 3/1 Preventing Infestations: Control Strategies and Detection Methods
• CCI Note 3/2 Detecting Infestations: Facility Inspection Procedure and Checklist
• CCI Note 3/3 Controlling Insect Pests with Low Temperature

Recommendations

• Maintain good housekeeping practices and keep collection areas clean. For additional protection in storage areas, keep basketry and other objects made of plant materials within closed storage units or drape them with tissue or lightweight plastic sheeting. In exhibit spaces, displaying the object within a case is preferable. If the object is on open display, then place it several metres away from the visitor route.
• Wear gloves, preferably close-fitting nitrile gloves, when handling objects. If powdery materials are found on the object, have the material identified. If it is toxic, consult with a conservator on handling procedures.
• Handle dirty objects as little as possible. Place the object on a support and move it by using the support. Dust, dirt and soot can detract from the visual appreciation of the object. These particles can also be abrasive and might attract pests. The following are some notes on the safe removal of dust, dirt and soot using a vacuum cleaner:
  • Ensure that the dirt does not indicate prior use (anthropological evidence).
  • Wear close-fitting gloves (nitrile or latex) and handle as little as possible.
  • Select a vacuum cleaner that has a power reduction device that allows reduced suction, or create reduced suction by drilling holes in the suction tube or attachment. Use a vacuum with high efficiency particulate air (HEPA) filtration, if possible. To prevent detached pieces from being sucked into the vacuum cleaner, cover the opening with netting or plastic screening secured with an elastic band or cord.
  • Work under good lighting.
  • Depending on the suction, hold the vacuum tube or attachment at approximately 8–20 cm (3–8 in.) from the object. There should be enough suction to remove the dust and dirt but not enough to lift any part of the object. Mini vacuum tools might be useful in cleaning intricate basketry.
  • Use a soft, clean brush (artist’s or cosmetic brush) to lift dirt from the object toward the vacuum nozzle. Continue over the whole object by moving slowly and methodically across its surface. Go over the surface again, lifting more dirt with a brush. To limit the danger of overcleaning, clean in repeated light passes rather than concentrating on one area. Overcleaning cannot be undone.
  • If the surface of the plant material is being disturbed, or if applied decorations are loosened and risk becoming detached, stop and consult a conservator.

Recommendations

• Keep plant materials away from windows. In display areas, reduce light levels to approximately 50 lux. This is especially important if the plant components are coloured.
• Keep lights off in storage areas when access is not needed. Place objects in enclosed cabinets or on draped shelving.

Incorrect temperature

High temperatures accelerate chemical reactions; conversely, lower temperatures slow them down. In the case of fibres dyed through a process using iron, iron-catalyzed deterioration, which makes the fibres become extremely weak and brittle (Figure 34), will occur at a slower rate if the ambient temperature is reduced. There can be benefits if the temperature is lowered by just a few degrees.

If higher temperatures result in low RH, plant materials become desiccated and brittle.

Waxes, gums or resins, applied to secure plant components, may become soft at high temperatures or brittle at lower temperatures, which might thus pose risks to the object’s structural integrity.

Incorrect relative humidity

At high levels of humidity, over 65% RH, mould can grow. Consult Figure 4 in Agent of deterioration: incorrect relative humidity, which provides a chart indicating the mould growth rate by humidity level.

Exposure to high humidity can soften some materials or cause distortion of parts that had been shaped while moist, then dried in position. If deteriorated binding elements soften, they might not be strong enough to secure the structure and distortions can ensue.

Baskets are made of elements that are tied, woven or otherwise intertwined, so their structure has built-in constraints. Large RH changes cause anisotropic swelling and shrinking of the fibrous materials (as described in Water), which can lead to distortions, breaks and losses. Such damage usually occurs first to the thinner weft elements that are wrapped or twined around larger warps or other elements (Figure 35).

Below 40% RH, plant materials become increasingly desiccated and brittle. At low RH, it is therefore important to provide good support and to handle the objects with extra precautions to prevent physical damage.