Woven papyrus sandals

Teresa K. Moreno <t.k.moreno [at] durham__ac__uk> writes

>I am looking for suggestions on how to go about cleaning and
>consolidating woven papyrus sandals....
>...
>The sandals are eventually going to go on display, and because of
>this they will need to be consolidated.  I am planning on running
>tests with various consolidants including cellulose ether, Mowilith
>DMC2 (PVA emulsion), PEG 1000, and PEG 1500.  Are there any
>suggestions regarding these or other consolidants?

Having little experience with woven papyrus and not being clear
about what the characteristics might be that require increases in
strength through consolidation, I've been a little hesitant to enter
the fray on this inquiry. I do have experience with archaeological
woven yucca leaf and retted yucca leaf fiber bundle sandals from
Southwest North America, (New Mexico and Arizona), generally
recovered from dry cave caches.

Archaeological monocot leaf and stem materials are, of course,
amazingly persistent, as a result of some of their resilient
constituents. Yucca leaves from all species have a thick epidermis
embedded with cuticular waxes composed of fatty acid esters, (very
stable, very persistent), collapsed cells and pectin which is key to
the stability of the leaf material because it is responsible for the
adhesion of the wax cutin to the cellulosic tissues. Perhaps like
yucca, the endodermis of the vascular stele of Cyperus papyrus stem
has a similar waxy/pectin composition that keeps fiber bundles
intact. This is fairly common to monocot stems. There are
extractives in the form of chromophoric compounds and phenyl
compounds . Besides giving the leaf materials specific color,
texture, gloss and mechanical characteristics, these materials also
provide resistance to IR and UV radiation, fungi and bacteria and
swelling of distinctive parenchyma and spongy collenchyma.

Structurally, of course, the fiber bundles associated with the
vascular proto- and meta xylem extra-cellular tubes are highly
crystalline, thick-walled, high tensile-strength sclerenchyma.
Cultivation, harvest and processing generally destroys the weaker,
less desirable characteristics and maximizes the desirable
characteristics of the plant material before incorporation into the
woven structure of the sandal. Wear, obviously, slowly deteriorates
the remaining desirable characteristics until massive failure is
reached, at which time the sandal is discarded or repaired. There
are also many sandals in the southwest that are designed for
ephemeral use, being composed of whole leaves with little processing
plaited quickly to form a sole and strap. Archaeological contexts
create there own deterioration environments.

So often what we are left with are the most persistent
characteristics of the plant material, in the case of yucca leaves:
cutin waxes, embedded pectin substances, crushed starchy collenchyma
and highly crystalline, but very extremely fissured thick-walled
sclerenchyma. Any consolidant would both need to have a chemical
and/or mechanical affinity for, and not cause deterioration to this
inclusive mixture of wax, carbohydrates, pectin, cellulose and
characteristic phytolyths and sclerids.

Since solvent-based consolidants quickly extract various fractions
of the waxy cutin, as well as extractives and are such large
polymers that they are only really capable of partially coating
extra-cellular gaps, tears and holes, you've got to be willing to
destroy some of the most characteristic qualities of the material,
analytically and the materials that provide the greatest protection
from swelling and physical deterioration in order to glob bits
together. Aqueous cellulose ethers, particularly ionic carboxymethyl
celluloses and their sodium salts, will have good bonding
characteristics, but ultimately will swell hemicellulose components
and cause much more fissuring of the cell wall materials in the
vascular fiber bundles--in effect, increasing the plasticity of the
material but lowering the tensile strength of the bundles--making it
weaker. PVA emulsions and acrylic suspensions will be a goopy/globby
mixture of both outcomes, at a tissue-component level of
observation. PEGs and gelatin are simply going to act as humectants,
accelerating the chemical and physical deterioration of the entire
package

So the question becomes, what are you trying to do? Are the
materials friable and powdering? That is probably separation of
endodermis waxes, pectin and collenchyma from the sclerenchyma
bundles. Are the materials brittle and snapping, fracturing, like
dried potato chips? That would be caused by the millions of fissures
in the crystalline cell walls of the structural sclerenchyma. In the
former case, you can reduce the powdering through consolidation with
cellulose ethers at the cost of dissolving some extractives and
accelerating the loss of tensile strength in the fiber bundles. In
the latter, 0.5 or 1% solutions of B-72 in acetone/ethanol may help
glue together fissured cell-walls, but at the cost of re-forming and
altering cuticular waxes. Because these sandals, in our case, our
relatively rare and culturally important, we usually opt to do
neither. While there have been rare occasions where important
structural elements have been consolidated to prevent loss or
breakage, we instead, cover sandals going on exhibition with sheer
silk crepeline of an appropriate color that is gathered and adhered
under a somewhat undersized sole-shaped cut-out of mat board.
Powdering and brittle fibers are both protected and contained and
the appearance is really perfectly acceptable and imperceptible on
exhibition. We do this frequently, even with some travelling
exhibitions and find it to be far more successful at true
preservation, sandal for sandal, than consolidation has ever been.
Best of Luck in your decision processes,


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                  Conservation DistList Instance 14:14
                  Distributed: Friday, August 18, 2000
                       Message Id: cdl-14-14-001
                                  ***