Polyethylene Glycol Treatments for Basketry on the Northwest Coast of North America

Ellen Carrlee* and Dana K. Senge

*ellen.carrlee@alaska.gov

Alaska State Museum

395 Whittier Street

Juneau AK 99801 USA

Abstract: Basketry artifacts discovered in wet sites have been routinely treated with polyethylene

glycol (PEG) since the 1960’s. Although the vast literature on PEG treatment of shipwrecked

wood informs the treatment decisions for this material, basketry treatments often do not behave

in the manner expected for waterlogged wood. This is in part due to the size and geometry of the

material, as well as the parts of the tree used, such as bark and root. A group of waterlogged

archaeological baskets at the Alaska State Museum provided the basis of an investigation into

better PEG protocols for treatment of this material. Ancient baskets treated with 20% PEG 400

and 5% PEG 4000 were not adequately stabilized for exhibition and study. Testing suggests

55% PEG 3350 is a better solution for the remaining baskets in this group still in need of

treatment, and consolidation with 10% Butvar B-98® in ethanol is effective in stabilizing the

fragile baskets that had previously been treated with PEG.

Keywords: polyethylene glycol, PEG, basketry, consolidation, Butvar, waterlogged,

archaeological

1. INTRODUCTION TO PEG TREATMENT FOR BASKETRY

Basketry artifacts discovered in water saturated archaeological sites (wet sites) on the Northwest

Coast of North America have been routinely treated with polyethylene glycol (PEG) since the

1960’s. These artifacts range in age from a few centuries to more than five thousand years old.

The vast literature regarding PEG treatment decisions focuses on the needs of shipwrecked

wood. Basketry treatments utilizing PEG often do not behave in the predicted manner of

waterlogged wood. This is in part due to the size of the woven elements of the basketry

structure, as well as the parts of the tree processed for the fabrication of these artifacts, such as

bark and root. The cellular structure of some basketry material, such as inner bark, differs

enough from trunk wood to require a variation in treatment (Florian 1982, Purdy 1996).

The ideal approach to treatment of archaeological basketry would be to assess the degree of

degradation before treatment and apply the proper PEG protocol. This can be more challenging

for basketry than for wood. One simple method is to air dry a small sample fragment and

observe shrinkage and deformation. Dramatic changes in dimensions from wet to dry can be

expected to correlate to a more deteriorated the cellular structure. Since the complex small

shapes made by the basketry weave can be difficult to measure accurately for comparison before

and after drying, photographing on graph paper can be useful technique. McCawley (1977) has

reported that waterlogged wood in sound or slightly degraded condition shows variation in

shrinkage in the three major directions: 0.5% longitudinally, 3-6% radially, and 5-10%

tangentially. For more deteriorated waterlogged wood, these differences are less distinct.

Another method to determine degree of degradation involves comparing the density of the

archaeological wood to the density of sound, non-waterlogged wood. Archaeological and

waterlogged wood is expected to be less dense because of the structure lost in deterioration.

Methods of quantifying this include the computer program PEGCON (Cooke and Grattan 1990),

and moisture content readings (Boone and Wengert 1998, Hamilton 1998). However, these

methods are less accurate with basketry than with wood. Measuring density is easiest with a

solid chunk of wood. Tiny woven basketry elements are challenging to measure accurately

because of the small size and geometry of the warps and wefts. Moisture content readings

cannot be considered accurate using equipment in a typical conservation laboratory because the

sample size available is so much smaller than recommended. For example, Boone and Wengert

(1998) recommend 100g of oven-dry sample to be used for measuring moisture content. While

this may be possible for waterlogged ship’s timbers, 100g is far greater than the sample

permitted for analyzing a basket, particularly since the analysis is destructive. The weight of a

generous basketry sample that might be available for testing is a mere 0.1 g dry weight (0.5g

fully waterlogged.) In addition to the tiny size, basketry is often made of root or bark, while the

reference standard is trunk wood.

Light microscopy has been used extensively to identify deterioration mechanisms in

archaeological wood. While conservators are trained in the principles and use of the polarized

light microscope, successful analysis of archaeological basketry can be difficult without

specialized training and practice. Most of the important references in the conservation literature

are authored by scientists with considerable backgrounds in plant anatomy and pathology. In

order to examine archaeological wood, familiarity with the structures present in sound wood of

the same species and part of the tree (root, branch, trunk) is needed (Friedman 1978, Florian et

al. 1990). Techniques used by experienced microscopists, such as examination under half

polarized light or fluorescence, and the use of staining may also be helpful (Florian et al. 1990,

Bjordal and Nilsson 2002).

In addition to a firm grasp of wood anatomy, an understanding of the various factors contributing

to archaeological degradation is needed to successfully interpret the images under the

microscope. Micromorphological changes include deterioration of layers in the cell wall, fungal

decay, bacterial attack, impregnation with foreign substances or staining from the burial

environment, missing or eroded structural elements, and even problems with sampling and

mounting techniques (Florian 1990, Hedges 1990, Blanchette et al. 1990, Blanchette and

Hoffmann 1994). It is difficult for a conservator who does not regularly work with wood

anatomy and archaeological material to make a confident analysis of archaeological basketry

with light microscopy. For example, secondary cell wall can sometimes look present when in

fact only amorphous granular residue remains (Hoffman and Jones 1990, Bjordal and Nilsson

2002). Caution is in order for determining degree of deterioration from light microscopy alone.

The conservation literature on the use of PEG to stabilize waterlogged wood indicates several

variables affect PEG treatment: deterioration of the basketry elements due to age, use and burial

environment, species, anatomical structure of the wood (bark, trunk, root etc), concentration of

PEG used, molecular mass of PEG used, duration of soaking, and heating during impregnation.

Low molecular mass PEG (PEG 200-600) is thought to penetrate more deeply into the secondary

cell wall and the smaller spaces in the wood than higher molecular mass PEG. It is also more

mobile and hygroscopic. If too much is used, the surface of the artifact will look wet, feel moist

and soft, attract dust, and be humidity-sensitive. High molecular mass PEG (PEG 1500-6000)

does not penetrate the secondary cell wall because the molecule is too large, but it acts like a

filler, impregnating the lumens and interstices between the cells. Too much high molecular

mass PEG can leave white crusts on the surface, result in a heavy artifact, and be more difficult

to dry. Higher molecular mass PEG is thought to cause structural damage if used on wood with

fairly intact cell wall structure, perhaps from the osmotic pressure as the hygroscopic PEG pulls

water out of the smaller structures where the larger PEG molecule cannot penetrate. (Grattan

1986, Hoffmann 1990). A combination of high and low molecular masses of PEG is often the

solution (Hoffmann1986, Johns 1998, Hoffmann et al. 2004) but it can be tricky to determine the

right mixture for solid wood, and basketry is even more challenging.

A review of the PEG literature and previous treatments at the Alaska State Museum suggests a

bias that basketry materials surviving in the archaeological context have intact secondary cell

wall structure that is available to be bulked. This bias would lead to treatment with low

molecular mass PEG. However, the results indicate that use of predominantly low molecular

mass PEG was not enough to impart the stability needed for study and exhibition.

2. PEG TREATMENTS AT THE ALASKA STATE MUSEUM

Much of the past PEG based treatment for waterlogged basketry on the Northwest Coast has

followed the lead of Gerald Grosso’s 50% PEG 1500 used on Ozette site material. PEG 1500 is

a combination of 41/59 weight percent mixture of PEG 300 and PEG 1450, with an average

molecular mass of 500-600. The name of the product was changed to PEG 540 Blend after

1976. At the Alaska State Museum, several PEG combinations have been attempted, and

comparison is informative, but limited. Caution is needed when comparing the results of

basketry that may be made of different materials, have differing degrees of deterioration, or

suffering from the all-too-frequent challenge of poorly documented treatments.

Fig 1: Castle Hill Basket slowly air-dried without impregnation with PEG

The Castle Hill Basket (Figure 1, 49-SIT-002) is thought to be spruce root and was excavated

damp but not fully waterlogged from a site dating to the Russian-American period (at least 150

years BP) in Sitka, Alaska in 1998. It was not impregnated but slowly air-dried in a refrigerator

with good results. It has an easily readable surface, slightly flexible woody feel and can be

easily handled or flipped for study.

Fig 2: Tawah Creek Basket treated with 50% PEG 540 at 60°C for one month

The Tawah Creek Basket (Figure 2, 49-YAK-019) is thought to be spruce root and was removed

from a waterlogged freshwater site in 2004 in the Yakutat area with fish weir stakes that were

radiocarbon dated approximately 130 years BP. It had a three-dimensional structure when

found, and retained that shape though treatment with 50% Carbowax PEG 540 Blend at 60°C for

one month. It was slowly dried at -35°C in a non-vacuum freezer. Surface appearance and

flexibility are adequate, although the broken edges could benefit from some additional

consolidation.

Fig 3: Spruce root lashings, 0.5cm wide, on the Montana Creek Fish Trap. Likely impregnated

with low concentrations of low, medium and very high molecular masses of PEG. Five of the

diagonal strips are painted Tyvek® reinforcing bands adhered with Acryloid B-72®.

The Montana Creek Fish Trap (Figure 3, 49-JUN-453) was found eroding from a riverbank near

Juneau, Alaska and excavated in 1989-1991. It was radiocarbon dated at 400-600 years BP. The

trap has sizable hemlock and spruce elements, but also basketry-like spruce root lashings.

Treatment notes suggest the trap was impregnated unheated over several months with 10% PEG

200, 5% PEG 1000 and 10% Carbowax Compound 20M. Polyethylene glycol Compound 20M

has an average molecular mass between 15,000 to 20,000 and is not typically used in

conservation. Its use at the Alaska State Museum was experimental based on a recommendation

and free sample from Dow Chemical Company. Due to its size, the trap was slowly air-dried

after impregnation. The trap materials fared very well, with no darkening, but the spruce root

was rather brittle and broken in many places. Small wads of Japanese tissue saturated with a

mixture of wheat starch paste and a small amount of polyvinyl acetate emulsion provided support

and adhesion for the spruce root lashings (Carrlee 2005).

Fig. 4: Detail of the Thorne River Basket under-treated with 20% PEG 400 and 5% PEG 4000 in

need of supplementary consolidation.

The Thorne River Basket (Figure 4, 49-CRG-433) was found as one large fragment in a

waterlogged site on Prince of Wales Island, Alaska in 1994 and radiocarbon dated 5450 years

BP. It was confirmed spruce root and treated with unheated 20% PEG 400 and 5% PEG 4000

over 6 months, then slowly dried at -35°C in a non-vacuum freezer. The basket has a pleasing

appearance but a soft, spongy rubbery quality. It sheds fibers readily and cannot be handled

without risk of breakage or unraveling the weave at the edges.

Fig. 5: Detail of one of the South Baranof Island baskets under-treated with 20% PEG 400 and

5% PEG 4000 in need of supplementary consolidation.

The South Baranof Island baskets from a waterlogged site in Southeast Alaska (49-XPA-78)

were radiocarbon dated at 4,550 years BP. Only one of the six baskets (Figure 5) from this site

has been treated; the other five remain waterlogged pending results of this study. The treated

basket was impregnated with the same protocol as the Thorne River Basket, with similar results.

Surprisingly, this basket was identified by plant anatomist Mary-Lou Florian as mountain

hemlock Tsuga heterophylla root instead of the expected spruce root. There is no known

tradition of weaving with hemlock root (Henrikson and Criswell 2009). The basket is in two

large fragments and about a dozen smaller fragments. Three of the smaller fragments were used

in this investigation to determine an appropriate consolidant for the under-treated Thorne River

and South Baranof Island baskets. Another waterlogged item from the 49-XPA-78 group, a

semi-rigid knotted netting artifact, provided sample material for exploration into a better

impregnation protocol.

3. TESTING HIGHER MOLECULAR MASS PEG FOR BASKETRY

3.1 Objectives of Testing

The shortcomings of the PEG treatment used for the Thorne River and South Baranof Island

baskets revealed the need for a better PEG treatment technique for the remaining baskets found

at the South Baranof Island site. A knotted spruce root netting artifact recovered in hundreds of

fragments provided sample material for testing various concentrations of high molecular mass

PEG. Reconstruction of this artifact is unlikely, and the large number of similar small fragments

give good comparative study samples. All fragments had been stored in distilled water in a

refrigerator since their discovery in 1995. Limited biological growth had occurred in the past.

Water was rarely changed. Since 2006, little biological growth has been noted. All fragments

were fragile. Extreme shrinkage and distortion to an air-dried fragment (figure 7) suggested

advanced deterioration. The testing aimed to answer the following questions:

Can we develop a PEG protocol that will make the waterlogged artifacts in group 95-12 stable

enough for study and exhibition?

What are the optimum concentrations of PEG for this basketry?

What are the optimum molecular masses of PEG for this basketry?

Will increasing the amount of high molecular mass PEG help?

Does heating during treatment provide a benefit?

Will the treated artifact be vulnerable to high humidity?

One set of samples was impregnated in a lab oven at 60°C to evaluate the potential advantages

and disadvantages of heating. Heating may speed and enhance penetration as well as the

solubility of high molecular mass PEG (Grattan and Clark 1987). However, heating was thought

to contribute to undesirable darkening for the objects treated at the Ozette site (Cooke, Cooke

and Grattan 1994). Heat is an accelerant to deterioration and PEG treatments for leather in the

literature have mostly eliminated heat altogether for that reason. Heat is also thought to break

down the PEG molecule, and some sources have advised against heating PEG during the

impregnation (Bilz et al 1994). Christensen (1970) found less osmotic collapse of oak using

PEG 4000 at room temperature than he did with heating. In both cases, no impregnation of the

oak core took place, but collapse only occurred in the hot bath. The Tawah Creek basket at the

ASM was heated with good results. (Carbowax PEG 540 Blend at 50% concentration for a

month at 60°C).

3.2 Selection of Concentrations and Molecular Masses

Samples fell into three main groups: samples treated at room temperature, samples treated at

60°C, samples treated briefly in a 160°C oven and then at 60°C. (This third grouping was the

result of an error that led the samples to be overheated for approximately 12 hours). Each group

had five fragments treated with various concentrations and molecular masses:

20% PEG 400, then 20% PEG 3350

Rationale: PEG 400 should enter the secondary cell wall and bond there, while the 3350 will fill

in the larger voids and give strength. This is slightly higher than the concentration of 3350 PEG

used previously on the South Baranof Island material, but that treatment did not give enough

strength. PEG 400 is kept at 20% to hopefully prevent excess from oozing out. Ozette site

material that was re-treated with 15% PEG 200 and 10% PEG 4000 was the subject of additional

consolidation tests with POLYOX® coagulant, suggesting the PEG treatment was not adequate

(Cooke et al. 1994).

20% PEG 400, then 35% PEG 3350

Rationale: High molecular mass PEG is supposed to perform well on highly degraded wood

(Hoffmann, 1984). The South Baranof Island basketry is very old and treatment with mostly low

molecular mass PEG was not fully successful. This suggests the basketry may be more degraded

than predicted, and may respond better to high molecular mass PEG.

20% PEG 400, then 55% PEG 3350

Rationale: Some references suggest avoiding the eutectic, but others (Jensen et al. 2002) seem to

suggest that aiming for the eutectic is desirable for even distribution. Theoretically, ice crystals

form in a way that blocks even distribution of the PEG unless the eutectic is used. Apparently,

concentrations lower than the eutectic also expand on freezing, causing cracks. At the eutectic,

the 9% expansion of ice is counterbalanced by 7% volumetric contraction of PEG. A medieval

log house in Oslo was treated successfully with 50-55% PEG 4000 (Astrup 1994). The

successful Tawah Creek basket treatment by Scott Carrlee (unpublished, Alaska State Museum)

used PEG 540 near the eutectic.

55% PEG 3350 alone

Rationale: Since the Jensen et al. article (2002) seems to suggest PEG near the eutectic is

optimal if an even distribution is the aim, even though other articles specifically indicate the

eutectic should be avoided, it would be worthwhile to isolate the PEG 3350 to test this. Perhaps

it simplifies the freezing process to only use one molecular mass of PEG. In addition, Astrup

(1994) and Hoffman (1990) found some success in their treatments with around 50% PEG 4000

in degraded softwoods. Strætkvern (2001) reported compression strength of wood is greater for

high molecular mass PEG treatments done without low molecular mass PEG.

20% PEG 400, then 75% PEG 3500

Rationale: Several sources report success with high concentrations of high molecular mass PEG

for highly degraded wood (DeJong 1978, Keene 1982, DeWitte et al. 1984, Jover 1994, Kaenel

1994).

3.3 Testing Protocol

Fragments of similar size with no obvious joins to other fragments were selected for testing and

photographed. Each sample was sewn between layers of nylon mesh screening with polyester

thread to hold the fragment securely, allow good circulation of solution around the fragment, and

permit handling. Each PEG concentration was increased incrementally approximately every two

weeks. PEG 400 was increased in 5% increments, PEG 3350 was increased in 5 or 10%

increments. In each case, the concentrations were increased gradually to minimize the risk of

osmotic shock from pressure differentials between the fluid inside the fragile wood and the fluid

in the container. The time to reach desired concentration took between 3 and 6 months. PEG

3350 was supplied as a powder and was dissolved in a bit of the test solution using a hotplate

before adding it to the unheated and heated sample containers. For the unheated samples, the

addition of the warm PEG 3350 caused them to be cloudy for two to three minutes before

becoming clear again. All samples were removed from solution at the same time. Each sample

was dipped in a beaker of distilled water to rinse excess PEG from the surface and gently tamped

with KimWipes® to remove as much water as possible before freezing. Fragments were

weighed and placed in a non-vacuum freezer (-35°C) to drive off the excess water through

sublimation (solid ice directly to vapor). Air drying without the freezer would send liquid water

to water vapor, and the strong surface tension of liquid water contributes to collapse of cell

structure as the water evaporates (Grattan 1986). Samples were regularly weighed to determine

the end point of drying (when weight no longer decreased,) and fragments were all removed

from the freezer at the same time. Concern about shrinkage or distortion during final air drying

required a method to compare the fragments at this stage to the final result. After removal from

the freezer, fragments were taken out of the nylon mesh and photographed on graph paper

immediately. They were photographed on graph paper again a week later to check for possible

distortion from the evaporation of residual water at room temperature (Figure 6). One month

after they were removed from the freezer, they were subjected to several 12 hour cycles of 80%

humidity to determine if the treatment rendered the fragments vulnerable to changes at high RH.

While the Alaska State Museum has stable RH, there are less stable locations in Alaska that may

wish to exhibit the artifacts after treatment. Exhibition and storage in uncontrolled humidity is a

reality for many PEG treated archaeological baskets.

Fig. 6 Fragment treated with 55% PEG 3350 at room temperature. Photographed on graph

paper immediately out of the freezer (left) and one week later (right) to check for distortion.

3.4 Results and Interpretation:

In this experiment, the percent weight loss in the freezer is used to interpret water loss and

possible impregnation with PEG (Table 1). Theoretically, in comparison to the air-dried control,

lower percent weight loss during drying means less water left in the system, indicating PEG

molecules replaced water molecules during treatment, reducing the amount of water that could

be lost from the structure during drying. According to this theory, all the room temperature

fragments had about the same amount of water loss after drying, and therefore a similar amount

of PEG penetration. At higher concentrations, the heated fragments had less water loss,

indicating better penetration of PEG 3350 than the room temperature samples. Possible

explanations of this greater penetration of molecules that may include: size variation through

thermal breakdown, better diffusion, possible expansion of wood structure with heat to allow

better penetration, or the enhanced solubility of heated PEG. Weight loss in the freezer for the

treated fragments ranged from 10% to 33%, compared to the air-dried untreated fragment which

lost 40% of its weight.

The samples with lowest concentrations were distinctly spongier to the touch than those

concentrations of 55% 3350 and higher, in spite of similar amounts of weight loss. Surprisingly,

results for 20% PEG 400 with 55% PEG 3350 were nearly the same as the results for 55% 3350

alone. Most of the samples showed very little dimensional change after final drying as revealed

by before and after photographs on graph paper. All were within a range acceptable for

successful treatment.

The waterlogged basketry elements (identified as spruce root) were dark brown in color when

waterlogged before treatment. After treatment, the samples treated at room temperature all

appeared a very pale beige-gray or driftwood-like color, with no obvious color difference with

higher concentrations. The samples treated at 60°C were all pale yellow ochre-grayish in color,

but still much paler than most historical basketry. The samples treated at 160°C then 60°C were

a rich brown burnt umber color, ironically more like historical spruce root basketry in color, and

samples treated with higher concentrations of PEG were darker in color. The untreated air-dried

control sample was the darkest of all (dark burnt umber in color) and extremely brittle, shrunken,

and deformed (Figure 7). Almost all samples had some whitish powdery PEG residue/crusts in

the crevices. This did not seem to increase with concentration, but was more pronounced on the

samples impregnated at room temperature. The waxy PEG could not easily be brushed from the

surface (the brush tended to drag it around) but localized application of ethanol with a brush

under magnification seemed to drive the PEG below the surface and improve the appearance.

All impregnated samples were placed in the humidity chamber and raised to 80% RH for 12

hours to evaluate effect of high RH on the concentrations and molecular weights of PEG used.

No oozing or surface changes were observed on the samples or on the blotter paper below them

during this first test. However, when the RH test was repeated, the unheated and the heated to

160°C samples that had been treated with the 75% PEG solution in water turned dark and waxy,

oozing PEG-like material. This did not revert back upon stabilization of the RH, and did not

seem to get worse with repeated RH tests. The sample treated with 75% PEG heated to 60°C did

not ooze or get dark, even on repeated RH fluctuations.

TABLE 1

PEG Concentration Results of treatment at

room temperature

Results of treatment at

60°C

Results of treatment at

160°C (12hours) and

60°C

20% PEG 400

20% PEG 3350

20 days at -35°C

22% weight loss in non-

vacuum freezer

65 days at -35°C

22% weight loss in

non-vacuum freezer

40 days at -35°C

33% weight loss in non-

vacuum freezer

20% PEG 400

35% PEG 3350

40 days at -35°C

23% weight loss in non-

vacuum freezer

90 days at -35°C

21% weight loss in

non-vacuum freezer

40 days at -35°C

25% weight loss in non-

vacuum freezer

20% PEG 400

55% PEG 3350

65 days at -35°C

23% weight loss in non-

vacuum freezer

90 days at -35°C

23% weight loss in

non-vacuum freezer

20 days, at -35°C

22% weight loss in non-

vacuum freezer

55% PEG 3350

90 days at -35°C

23% weight loss in non-

vacuum freezer

65 days at -35°C

18% weight loss in

non-vacuum freezer

20 days at -35°C

22% weight loss in non-

vacuum freezer

20% PEG 400

75% PEG 3350

90 days at -35°C

20% weight loss in non-

20 days at -35°C

10% weight loss in

65 days at -35°C

18% weight loss in non-

vacuum freezer non-vacuum freezer vacuum freezer

Fig: 7: These waterlogged archaeological basketry samples test increasing concentrations of

PEG 3350. Concentrations increase from left to right, with top row representing unheated,

middle row heated to 160°C then 60°C, and bottom row heated to 60°C. Untreated air-dried

sample in upper right.

4. TESTING CONSOLIDANTS FOR UNDER-PEGGED BASKETS

4.1 Objectives of Testing

Identifying a good consolidant for the undertreated baskets was challenging because materials

that might consolidate wood well are not the same as ones that are expected to bond well to a

waxy surface such as PEG. A review of the literature indicated that many of the adhesives said

to bond well with PEG are not conservation-friendly. These included casein glues, hide glues,

hot-set phenolic resin, cold-set urea resin and resorcinol resin (Stamm 1959, Mitchell 1972).

Empirical testing was carried out to examine various potential consolidants commonly available

to conservators and archaeologists.

4.1.1 Testing Protocol

The testing done was empirical in nature, meant to narrow down the possibilities to test on

fragments of the underPEGged basketry. Rice (1990) thinks that PEG chemically interferes with

the formation of bonds between the wood and the adhesive and that PEG gets in the way of

further consolidation with polymers such as acrylics. Testing the bond of potential consolidants

with PEG was one aspect of the empirical testing. PEG 3350 was placed in a disposable

aluminum weighing pan on a hotplate over low heat. Patches of molten PEG 3350 were brushed

onto the ends of two glass microscope slides and allowed to cool. The two patches were then

adhered with a drop of test adhesive. The free end of the top slide was supported by a blank

slide. After drying overnight, the supporting slide was pulled out to cause slight stress on the

join and identify the weakest bonds. Then one slide was picked up and shaken manually to test

the strength of the bond. Finally, the slides were manually pulled apart. Under magnification,

each adhesive was picked at with a sharp tool to test how easily it might peel off the PEG. The

test on glass slides was repeated a second time. An identical test was done with molten PEG

3350 on the surface of flat wooden sticks. Several products were tested that are not ideal for

conservation but may be tempting to archaeologists. Hide glue, cyanoacrylate, wood glue, and

cellulose nitrate were tested because they are mentioned in the hobbyist literature concerning

PEG and green wood and they are more widely available than adhesives which have good aging

properties and are readily reversible. Of those four adhesives, only cellulose nitrate (Duco®)

performed at the level of the final samples.

Results narrowed the field of choices to seven: Acryloid B-72®, AYAT®, Butvar B-98®, BEVA

D-8 dispersion®, Acrysol WS-24®, Lascaux Medium for Consolidation®, and POLYOX®

WSR coagulant. These seven were then tested on silk crepeline and gossamer nylon fabrics by

both pipette dropper and brush application to see how the consolidants might penetrate small

spaces in the textile weave and to reveal qualities of flexibility and glossiness. The final five

consolidants were applied by brush on five small fragments of the South Baranof Island basket

that had been under-treated with PEG. Samples needed to be flipped frequently during drying to

avoid pooling of consolidant on the underside.

4.1.2 Results and Interpretation

Samples that failed at the bond between the two patches of PEG on the glass slides and the

wooden sticks were interpreted as weaker than samples that failed at the PEG/substrate bond.

Samples that did not penetrate into the PEG but formed a skin were considered poor candidates.

Consolidants tested on the fabric were examined for gloss, penetration, and flexibility. On the

archaeological basketry, samples were examined for gloss, darkening, and flexibility in addition

to stabilizing the fragile structure.

4.2 Promising Consolidants Tested on Basketry Fragments

4.2.1 Butvar B-98®

Several sources (Grattan 1980, Sakuno and Schniewind 1990, Schniewind 1990, Spirydowicz et

al. 2001) suggested Butvar B-98® might be successful on archaeological wood not treated with

PEG. Tímár-Balázsy et al. (1998) reports that on textiles, polyvinyl alcohols and polyvinyl

butyrals can get stiffer and the textiles are said to suffer frictional damage from the sharp edges

of the particles when the adhesive become aged, rigid, and cracked. Sakuno and Schniewind

(1990) found the adhesive strength of Butvar B-98® higher than Acryloid B-72® and AYAT®

but less than PVA emulsion. Schniewind and Carlson (1990) also mention that Butvar B-98® is

better than Acryloid B-72® for strength. In the Alaska State Museum testing, 10% Butvar B-

98® in ethanol was the best consolidant choice (Figure 8). It had among the strongest bonds of

all adhesives tested, although weaker on the wooden stick than on the glass slide. It did seem

stronger than Acryloid B-72® when manipulated with the fingers. It penetrated the fabric well,

looked slightly glossy, and was flexible without being brittle, but not as flexible as Lascaux

Medium or Polyox. No noticeable darkening occurred, and the physical appearance of the

basketry was the best of the five consolidants tested on basketry. Butvar B-98® is a polyvinyl

butyral resin manufactured by Monsanto and available through Talas in the U.S.

Fig 8: South Baranof Island basket fragments under-treated with PEG. Top fragment

consolidated with Butvar B-98® 10% in ethanol and bottom fragment unconsolidated.

4.2.2 Acryloid B-72®

Fig. 9: South Baranof Island basket fragments under-treated with PEG consolidated with 10%

Acryloid B-72® in 50:50 acetone and ethanol.

Acryloid B-72® has been recommended as a consolidant for deteriorated archaeological wood

not treated with PEG by several sources (Grattan 1980, Wang and Schniewind 1985, Sakuno and

Schniewind 1990, Schniewind 1990). It also performed well in the reconstruction of an

archaeological fish trap treated with PEG (Carrlee 2005). 10% Acryloid B-72® in 50:50 acetone

and ethanol was tested empirically at the Alaska State Museum and seemed to be the strongest of

all consolidants tested on the PEG-treated basketry (Figure 9). It penetrated the fabric well,

looked slightly glossy, and was flexible without being brittle, but not as flexible as Lascaux

Medium or POLYOX. Some darkening occurred and the surface of the basketry was slightly

glossy. Acryloid B-72® is an ethyl methacrylate (70%) and methyl acrylate (30%) copolymer

manufactured by Rohm and Haas and available through Talas in the U.S.

4.2.3 AYAT

Grattan (1980) did not test AYAT®, but listed AYAC® as his third choice of consolidant for dry

and degraded wood (not PEG treated) after polyvinyl butyrals and acryloid resins. Schniewind

(1990) tested AYAT® on degraded archaeological wood (not PEG treated) and felt it was not

hard enough, only penetrated the surface layer, and caused a notable deepening of color. In the

Alaska State Museum testing, 10% AYAT® in ethanol was one of the better consolidant choices

(Figure 9) and had the best handling properties, flowing smoothly off the brush and wicking

visibly into the basketry fibers during application. On the glass and wood mock-ups, it was

almost as strong as Acryloid B-72® or Butvar B-98® and penetrated into the PEG. It also

penetrated the fabric well, looked slightly glossy, and was flexible without being brittle, but not

as flexible as Lascaux Medium® or POLYOX®. No noticeable darkening occurred, and the

physical appearance of the basketry was similar to the excellent appearance of Butvar B-98®

tested on the basketry. The AYAT® tested was part of the series of polyvinyl acetate resins

manufactured by Union Carbide until recently, and the same as the product mentioned by

Grattan (1980) and Schniewind (1990). However, the products marketed today through

Conservation Support Systems and Talas in the U.S. may not be the same AYAT® available in

the past (Alderson 2008). Investigating the performance of the new AYAT® may be an avenue

of future research.

Fig. 10: South Baranof Island basket fragment under-treated with PEG consolidated with

AYAT® 10% in ethanol

4.2.4 Lascaux Medium for Consolidation®

Lascaux Medium for Consolidation® has not been mentioned in the literature for this

application, but behaved well during the empirical tests. It was used in full concentration as

supplied, and penetrated the fabrics very well. It dried with slight gloss, and was one of the few

samples to fail at the PEG-glass bond instead of the PEG-adhesive bond. However on the

basketry samples it was unacceptably dark and glossy with a rubbery, plastic-like quality when

manipulated with the fingers (Figure 10). It also formed a skin in some interstices of the

basketry, and formed some areas of glossy pooled excess in spite of frequent flipping of the

fragments during drying. Lascaux Medium for Consolidation® is an aqueous dispersion of

acrylic co-polymers based on acrylic ester, styrene, and methacrylate ester manufactured by

Lascaux Colours and Restauro in Switzerland and available through Talas in the U.S.

Fig 11: South Baranof Island basket fragment under-treated with PEG and consolidated with

Lascaux Medium for Consolidation®.

4.2.5 POLYOX® WSR Coagulant

POLYOX® has been used on archaeological material with good results (Bilz et al. 1991, Cooke

et al. 1993). During testing, POLYOX WSR coagulant 2% aqueous solution formed a stringy

mess with very poor handling properties. It was not sticky but made long slimy strings that

could not easily be broken. However, it seemed to penetrate well into the PEG and form a

moderate bond on both wood and glass samples. It also penetrated the fabric very well and dried

with little gloss. On the basketry, POLYOX® darkened the surface slightly, had a slight gloss

and formed a distracting skin in some interstices of the weaving (Figure 12). The POLYOX®

fragment was still very flexible and felt the most fragile of the three fragments tested on basketry

fragments when manipulated with the fingers. The product literature suggests mixing in a 1%

solution, which may have better handling properties, but as a 2% solution was still too fragile a

1% solution was not attempted. POLYOX® WSR coagulant is a non ionic polyethylene oxide

with a molecular mass of 5,000,000 g/mol manufactured by Dow Chemical and provided as a

free sample.

Fig. 12: South Baranof Island basket fragment under-treated with PEG consolidated with 2%

POLYOX® WSR coagulant.

4.3 Other Consolidants Examined

Acrysol WS-24® took a long time to fully dry, but had moderate penetration of PEG and a

moderate bond. When tested on fabrics, it was glossy, formed bubbles that dried in place, and

formed a stiff film that cracked when flexed. Acrysol WS-24® is often used on archaeological

bone.

BEVA D-8® dispersion made a moderate-to-weak bond, and formed a skin that separated

readily from the PEG. Further testing on fabric revealed good flexibility but poor penetration,

with drops made by the pipette drying in place as droplets on the surface.

Carbowax PEG 3350 failed to bond well on both glass and wood tests, although molten high

molecular mass PEG has been frequently mentioned as a surface treatment for artifacts stabilized

with PEG (Grattan 1982, Grattan and Clarke 1987, Singley 1988, Muncher 1991, Rodgers 1992).

CM Bond M-4® formed a moderate bond and seemed to partially penetrate into the PEG but

also formed a skin that separated readily from the PEG.

Jade 403® PVA emulsion was part of the treatment used by Carrlee (2005) for spruce root

lashings of a fish trap treated with PEG. In the current testing, it formed a moderate bond and

seemed to partially penetrate the PEG, but did not dry well.

Klucel G® penetrated well but was weak in all tests at both 2% and 20% in ethanol. It has been

mentioned in treatment of archaeological wood not treated with PEG by Caple and Murray

(1994) and Park (1997).

Lascaux 498 HV® penetrated into the PEG and did not form a separate skin but had a moderate-

to-weak bond.

Rabbit skin hide glue gave a poor bond, did not penetrate well, and was noticeably yellow. Hide

glues had been mentioned in the literature by Stamm (1959) and Rice (1990).

Super Glue® (cyanoacrylate) did not penetrate well and formed a separate skin. It made a

moderate but brittle bond. Has been mentioned in the literature by Zumpe (1981).

Titebond II® wood glue penetrated little, had a poor bond, was slow to dry fully, formed a

separate skin that readily slid off the PEG and was noticeably yellow. Mitchell (1972) did not

think PVA’s worked well to bond wood treated with PEG and Stamm (1959) thought they gave

decreasing strength with increasing PEG concentration. Grattan and Clarke (1987) suggested

PVA emulsions with a little bit of PEG aided bonding PEG treated wood.

Duco® (cellulose nitrate) made a moderate bond on the glass and wood samples and penetrated

well, but lacks good aging properties (Stark 1976).

5. CONCLUSIONS

For the ancient waterlogged basketry from the South Baranof Island site, 55% PEG 3350 is the

best solution for stabilization. The idea that high molecular mass PEG at around 55%

concentration is useful for highly degraded softwoods is in harmony with the conclusions found

by others (Astrup 1994 and Hoffmann 1990). This may indicate that these basketry pieces are

more degraded than previously thought, with little secondary cell wall available for bonding with

low molecular mass PEG. The survival of this material may be due in part to the tenacity of the

lignin. Lignin is often the predominant structural element in archaeological wood (Hedges

1990). In addition, lignin content is typically higher in softwoods than in hardwoods (Bidlack et

al. 1992) and softwood lignin is less easily degraded (Hedges 1990). Ideally, degree of

deterioration ought to be determined before treatment in order to guide the proper protocol, but

this can be difficult and treatment is often done based on previous examples from other sites.

The diminutive size, irregular geometry, and very light weight of basketry fragments make

accurate measurement of density and moisture content difficult. In cases where PEG treatment

has not afforded adequate stability, 10% Butvar B-98® seems to offer enhanced stability without

brittleness or changes in surface appearance. Acryloid B-72® and AYAT® resins may also hold

promise. One of the few references on adhesives for PEG (Rice 1990) recommends solvent-

borne systems that can dissolve into the surface of the PEG, and solvent borne systems did

perform better in the testing on the basketry fragments than aqueous systems. Ongoing research

by the authors seeks to determine if examination of archaeological spruce root and cedar bark

basketry with light microscopy is adequate to determine degree of degradation and predict

correct treatment strategies with PEG. The authors are also compiling a reference of

archaeological basketry treatments one the Northwest Coast of North America to help inform

future treatment of this material. This work will be presented at the 2010 annual conference of

the American Institute for Conservation. An annotated bibliography of articles relevant to PEG

basketry conservation is available at http://ellencarrlee.wordpress.com

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