FUNORI: OVERVIEW OF A 300-YEAR-OLD CONSOLIDANT
JOSEPH R. SWIDER, & MARTHA SMITH
ABSTRACT—Funori, a product from seaweed found mostly in Japan, has been used as an adhesive and a consolidant for centuries. Many conservators are familiar with funori but may be unaware of its chemistry and reliable methods for its preparation. Funori has been used successfully for decades at the Freer Gallery of Art and Arthur M. Sackler Gallery's Department of Conservation and Scientific Research in the paper, East Asian paintings, and object conservation laboratories. This article is a review of the conservation and scientific literature to give conservators insight into the chemistry of funori and related seaweeds and to propose methods for its preparation.
TITRE—Le funori: un consolidant utilisé depuis 300 ans. RÉSUMÉ—Le funori, un produit dérivé des algues que l'on retrouve surtout au Japon, a été utilisé comme adhésif et consolidant depuis des siècles. De nombreux restaurateurs utilisent le funori, mais connaissent peu ses propriétés chimiques ainsi que des procédés fiables pour sa préparation. Le funori a été utilisé avec succès depuis plusieurs décennies aux laboratoires de restauration des papiers, des peintures asiatiques et des objets de la Freer Gallery of Art/ Arthur M. Sackler Gallery (musée d'art Freer/galerie Arthur M. Sackler). Cet article présente une revue des publications dans les domaines de la science et de la restauration, dans le but de fournir aux restaurateurs quelques réponses sur les propriétés chimiques du funori et autres algues, et afin de proposer des méthodes adéquates pour sa préparation.
TITULO—Funori: vision general de un consolidante de 300 años. RESUMEN—El funori, un producto de algas marinas que se encuentran mas que todo en el Japón, ha sido utilizado durante siglos como adhesivo y consolidante. Muchos conservadores tienen familiaridad con el funori pero pueden no conocer su composición química y los metodos confiables para su preparacion. El funori ha sido utilizado exitosamente por décadas en el Departamento de conservación e investigación científica de la Freer Gallery of Art/Arthur M. Sackler Gallery (Galeria de arte Freer/Galeria Arthur M. Sackler), en los laboratorios de conservación de papel, de pinturas del este asiático y de objetos. Este artículo es una reseña de la literatura de conservación y científica con el objeto de proporcionar a los conservadores una visión general sobre la química del funori y otras algas marinas semejantes y para proponer metodos para su preparación.
TÍTULO—Funoroi: Observações Gerais dos 300 Anos Do Consolidante. RESUMO—Funori, um produto de algas encontradas basicamente no Japão, tem sido utilizado há séculos, como adesivo e consolidante. Muitos conservadores estão familiarizados com o funori, mas talvez desconheçam sua química e métodos confiáveis para seu preparo. Funori tem sido utilizado com sucesso por décadas na Freer Gallery of Art and Arthur M. Sackler Gallery's Department of Conservation and Scientific Research (Galeria de Arte Freer, Departamento de Conservação e Pesquisa Científica Da Galeria M. Sackler) nos laboratórios de conservação de papel, de pinturas do Leste Asiático e de objetos. Este artigo é uma revisão da literatura científica e de conservação para dar aos conservadores informações sobre a química do funori e algas relacionadas e tambem propor métodos para seu preparo.
Over the last century conservation has seen an abundance of synthetic consolidants for adhering flaking paint and mending small fractures. The seaweed product funori, first used more than 300 years ago, is still produced today and can rival many other traditional and synthetic consolidants for its ease of use in a nontoxic form. Although funori has been employed for many years, references to its use and study are scarce. This article surveys the conservation and scientific literature on the use and chemical properties of funori. Preparation guidelines are provided for those who use funori or desire to experiment with it in their laboratories.
Funori is extracted from any of three species of red seaweed found mostly on the coasts of Japan: Gloiopeltis tenax (mafunori), Gloiopeltis complanata (hana-funori), or Gloiopeltis furcata (fukuro-funori), collectively referred to as the funorans. It is first recorded in Japan in 1673 as a size for textiles and papers and even as a cement for tiles and building materials (Chapman 1980). The seaweed is cultivated on rocks in Japan and is produced year-round. Processing funori is minimal: it is washed and soaked to remove debris and salts (fig. 1). Many modern processes use a bleaching agent such as potassium hydroxide or sodium peroxide after soaking, lightening the color of the seaweed to an orange-yellow. The fibers are shaped into mats, traditionally placed in the sun for further bleaching, and the dry mats are cut and rolled.
2 SCIENTIFIC SURVEY
Processed seaweeds easily dissolve in water, and their swelling and colloidal nature make them commercially useful. Seaweed gums are natural carbohydrate polymers, composed of repeating units of saccharides (sugars). Traditional seaweed taxonomy is based on qualities such as color, structural properties, and odor (Stancioff 1980). Red seaweeds of the family Rhodophyta are loosely defined by their color, and subsequent classification has been based on chemical structure and origin. Rhodophyta are grouped into three types: agars, carrageenans, and porphyrans. Funori is considered a subset of agars; however, because its chemical and structural qualities are close to those of carrageenans, our study will focus on both agars and carrageenans. Porphyrans, not used commercially or in conservation, will not be discussed.
Agar comes chiefly from the two species Gelidium and Gracilaria, and its largest commercial producer is Japan, where it has been cultivated since the 17th century (Percival and McDowell 1967). The many commercial advantages of agar include its ability to gel at a low concentration (as low as 1%) and at room temperature, and its resistance to microbiological agents and most simple enzymes (Araki and Arai 1955; Araki 1965; Meer 1980). Most carrageenans belong to the Chondrus and Gigartina species found on the northern coasts of most countries in the world. These two types of Rhodophyta are based on variations of the monosaccharide galactose (fig. 2) and referred to as the galactans of the Rhodophyta.
Polysaccharide chains in agars and carrageenans are based on two repeating forms of galactose, ß-D-galactose and an anhydride form, 3,6-anhydro-α-L or D-galactose (fig. 3) that form a double helix. Traditionally,
Commercial funori before use
the distinction between agar and carrageenan is based on stereochemistry: the carrageenan polysaccharide has both monomer galactose units in the D-form, while agar has the anhydride in the L-form. Both polysac-charides are linked by alternating ß1P4 and α1P3 links (fig. 4). In addition to the stereochemical difference, carrageenans are highly sulfated, whereas most agars have trace sulfates at most. Funori is a link between the two types: it contains the agar 3,6-anhydro-α-L-galactose but is sulfated like the carrageenans, although to a lesser degree.
Recent scientific studies have separated funori into structurally homogeneous fractions to better understand its structure and taxonomy. The fractions indicate the amount (usually in percent of the entire carbohydrate polymer) of a common unit or homogeneous monomer in the seaweed, i.e., a fraction of 3,6-anhydro-α-L-galactose. In general, the most variation among species is in the amount of anhydride (Hirase and Watanabe 1971; Takano et al. 1999). Like funori in its native state, none of the fractions gel. The same methods of fractionation on carrageenan revealed structural similarities to funori (Takano et al. 1998), notably that funori fractions were found in carrageenan polysaccharides. Recent studies point to the fact that carrageenan “backbones,” or the 3,6-anhydro-α-D-galactose sulfated components, were also found in funorans (Takano et al. 1999).
Three forms of cyclic galactose known as galactopyranose: (a) ß-D-galactopyranose; (b) 3,6-anhydro-α-D-galactopyranose; (c) 3,6-anhydro-α-L-galactopyranose
(a) ß-D-galactopyranose-(1P4)-α-D-galactopyranose; (b) α-D-galactopyranose-(1 3)-ß-D-galactopyranose
This similarity should be kept in mind when comparing the physical properties of the agars and funori with the carrageenans, in particular for solubility and gelling. The carbohydrate chains of red seaweeds line up together in a “hollow helix” structure (Lobban and Wynne 1981), with side groups of each unit influencing gelling ability. Agar, empty of sulfate groups, will gel at low temperatures and at low concentrations because the helical structures are able to pack tightly due to lack of electrostatic and steric hindrance (Duckworth et al. 1971). Carrageenans and funorans contain sulfate groups that cause the helices to repel one another; although viscous, they do not readily gel. Unlike funori, carrageenan has been commercially available for decades and is routinely separated and sold as fractions under Greek prefixes (i.e., K-i,-6-), each for a different application (i.e., food additives, marbling). Carrageenan is sold commercially as a powder with a cationic salt added (usually the infraction) to remove the sulfate repulsion and form a gel with the cation as a counterion for the sulfate groups. Although not previously reported in the literature, our laboratory has shown that funori will also gel with salts (i.e., potassium chloride) in approximately the same concentration as typical commercial carrageenan. In addition, funori was heated in both tap and deionized water. Neither heat nor water type had an effect on the pH.
Scientific studies that have attempted to sulfate polysaccharides such as agarose, starch, and porphyrans having no sulfate groups showed that C-6 is the preferential site for sulfate substitution (Takano et al. 1996). Consequently, this is the site normally sulfated on the funorans but not on the carrageenans, possibly because the C-6 placement is more sterically favored in funori. Although this specificity could imply greater reactivity for the funorans on treated materials in terms of sulfuric acid production, these seaweeds have never been shown to be acidic and this addition may be beneficial as protection. Because of this unique structure and composition, funorans have shown promise as an antitumor agent and as a mouthwash, owing to their apparent antimicrobiological activity (Ren et al. 1994; Ren et al. 1995; Saeki et al. 1996). That there is no record in the literature or in our laboratories of microbiological attack on funori-treated artifacts somewhat supports this antimicrobiological property, but further scientific studies are warranted. When these seaweeds (mostly carrageenans) are used as food additives, a polysaccharide with greater anhydride character is used for gelling applications whereas one with less anhydride and more sulfate character is employed for a viscous solution (Percival 1970). It could be concluded from the above information that funori typically having a single sulfate constituent and anhydride per unit may strike a balance and create an optimal consolidant.
3 LABORATORY STUDIES ON FUNORI PREPARATION
A survey of the conservation literature reveals a number of funori preparations, which are compiled in table 1 together with preparations used at the Freer and Sackler Galleries. In the scientific studies previously mentioned, raw funori is usually washed and given no further alkali treatment, as is typically done with carrageenans. Some methods only add funorans to boiling water (Takano et al. 1999); others soak and macerate it in a blender before adding it to boiling water (Takano et al. 1995; Takano et al. 1998). Many references in the conservation literature fail to give specific methods of preparation (Higuchi 1979; Oka 1988). Some references indicate a solution between 1% and 5% (Masuda 1984; Keyes 1986; Horie 1990; Kariya 1995) but do not provide dilution factors or a purchase origin.
The fact that funori is seldom treated before being sold to conservation studios casts doubts on its purity for use on cultural artifacts. Agar has been purified and separated for decades by a simple freeze-thaw method (Grabar 1959; Sewer 1983). As it thaws, agar remains a gel at room temperature while the water in it melts and is removed, presumably containing excess salts. Our freeze-thaw tests on funori showed that like most carrageenans, it cannot be purified by this method. We attempted to purify funori to produce a solution that was free of pulp and obvious extraneous material. A stock solution of 2% dry funori in distilled water (weight per weight) was heated at about 90°C for one hour and stirred occasionally. We used vacuum filtration with Whatman no. 1 filter paper, adding approximately 15 ml at a time because the filter quickly became clogged. The filtered product was clear of most fibrous pulp and other debris, and tinted slightly amber. It was almost clear when painted out on glass. It is a common practice in seaweed studies to precipitate a seaweed solution with ethanol, and we tested this practice as a final step. When approximately three times the filtrate volume
Funori Preparation Methods from Conservation and Commercial Sources
of absolute ethanol was added to the filtered funori and stirred, a white, stringy precipitate immediately formed. The precipitate was dried on glass and dissolved easily in room temperature distilled water much like the funori prepared without ethanol precipitation. There was no clear advantage to using the ethanol precipitation step, except that the funori seemed to dry slightly faster.
Our laboratory purchased commercial funori and prepared it in a variety of ways to see if there was one standard “best” method. We divided the process into six stages: rinse, soak, heat, extract, dry, and reconstitute.
- Rinse: Although there is no evidence that salts and minerals are a problem, rinsing dry funori under dripping water (tap, deionized, or distilled) for 15 to 30 minutes is a reasonable precaution even though some of the soluble matter is lost in the process. This precaution has been confirmed in other studies (Michel et al. 2002).
- Soak: A solution forms faster during heating if the funori is soaked at room temperature or in a refrigerator for eight or more hours or overnight.
- Heat: Funori soaked in cold (not heated) water makes a dilute solution with weak strength. Heating it at or just below a simmer (about 60–90°C) for 60 to 90 minutes produces a more concentrated solution. Heating it longer than 90 minutes does not appear to extract additional material. Boiling does not weaken the tack of the funori, but a lower temperature lessens the danger of fast evaporation and burning. Water can be added during heating to prevent burning or to thin the solution.
- Extract: Clean, undyed fabric or a fine mesh plastic strainer can be used as a filter. Two to four layers of clean cheesecloth will filter out many fibers. Further filtering through silk or other fabrics with finer weaves will remove more fibers. Centrifuging or filtering with an aspirator vacuum through Whatman no. 1 filter paper removes even more fibers and leaves a pale, slightly cloudy solution that is aesthetically pleasing but not necessarily more useful. Vacuum filtration produces almost the same results as filtering through both cheesecloth and silk. As is done with many seaweeds, funori can be precipitated in absolute ethanol to produce a white, stringy precipitate. Salt is not needed to facilitate precipitation, though it is commonly used with agar precipitation. A solution of prepared funori can be kept under refrigeration for a short while until it begins losing its stickiness or grows mold.
- Dry: After heating, the solution can be poured onto clean glass, silicon-coated Mylar or Formica (Coombs 2003), where it forms a thin layer that can be scraped or peeled off when dry. Ethanol-precipitated funori can also be peeled off Formica or scraped off glass. Dry funori is difficult to remove from Mylar and saturates silicone-release paper. In our laboratories the dry, prepared funori has a shelf life of up to four years.
- Reconstitute: Dried prepared funori is easy to cut up and reconstitute to a desired concentration. It will dissolve in room temperature water in about 10 minutes (faster in hot water) and overnight in a refrigerator.
Preparing funori is a flexible procedure, and overall our attempts successfully produced a material that was free of debris and suitable for treating artifacts.
4 USES OF FUNORI IN CONSERVATION
The same flexibility applies to the ways in which funori is used, normally for applications that require a low-strength consolidant, usually on paper. The advantages of funori as a consolidant are many: it has good penetrating ability and wets surfaces easily, dries matte, can be diluted with water, and is nontoxic. Uses for funori in conservation include sizing paper and textiles; consolidating flaking and powdering paint; repairing and facing East Asian painting and works on paper (Keyes 1986; Smith 1990); repairing silver and gold leaf and mica (Higuchi 1979; Kariya 1995); backing paintings when mixed with animal glue (Oka 1988); and repairing the structure of wooden objects (Tsujimoto 1979). In Japan it has been used to adhere tiles and paper to walls and as a cement in plaster wall construction and in porcelain decoration. Most authors note the advantages of funori as a low-strength consolidant with low surface tension and low gloss (Higuchi 1979; Michel et al. 2002). One study has examined its effects over time with artificial aging (Michel et al. 2002). This study examined changes in gloss, color, and mechanical strength of funori that underwent a typical artificial aging regime of accelerated light, temperature, and humidity. The funori was shown to bleach more under the extreme light conditions, becoming slightly more brittle but still flexible. Although the artificial aging experiments are encouraging, we stress that the long history of funori-treated objects without note of its failure or discoloration is more creditable.
To confirm funori's properties, we have examined previously treated artwork in the Freer Gallery of Art, where funori is used in paper and East Asian painting conservation regularly. A concentrated solution of funori is made up and thinned to suit the treatment at hand. Often the funori is applied in thin layers until the treatment is complete. For consolidation, all that is required is funori added to the edges of flaking paint and the flakes held down to secure. We recently examined several objects treated between 1975 and 1980 and compared their present state to their original treatment records.
- Chinese wood sculpture, Southern Sung, acc. no. F1974.6: The entire surface was brushed with funori to consolidate flaking paint. It is noted that other portions of the statues required stronger consolidation on the wood base where losses were evident. In these cases Paraloid B-72 was employed.
- Japanese wood sculptures, Kamakura period (1185–1333):
- Acc. no. F1974.20: Funori was brushed over the entire surface of each figure in 1977 to consolidate flaking pigment and gilding. In 2002, funori was again used to consolidate some spots of lifting paint to be compatible with the earlier treatment. According to the records, the gilding did not respond to the funori treatment at this time and was treated with Paraloid B-72.
- Acc. no. F1977.19: The entire surface was brushed with funori to consolidate flaking paint and gold. It was noted in this treatment that areas that required more layers of funori could not be treated before the previous layer was dry. The gilding had to be held in place while drying.
- Acc. no. F1978.28: Funori was used on this object to consolidate powdery pigment and paint that was hanging on. A stronger consolidant was required for structural consolidation where funori was too weak. 2d. Acc. no. F1976.12: As with the other wooden statues, funori was originally used to consolidate the entire surface of the object-paint and gilding. Funori was applied again in 2002 prior to exhibition, but the gilding required Paraloid B-72 for consolidation where the funori was ineffective.
- Indian painting on textile, Mughal period, ca. 1570, acc. no. F1949.18: In 1977 a thin solution of funori was applied to much of the painting to consolidate the flaking paint, followed by a thicker solution on the white or pastel areas that were more likely to flake off with time. An additional funori treatment was required a month later, and no further treatment was required.
No color shifts were noted in the treatment records. Visual examination of the objects at the present time and comparison with previous photographs showed no color change. Funori continues to be used as a consolidant, adhesive, and poultice material, especially on Asian and Near Eastern works of art on paper.
The persistence over the centuries of funori as a useful adhesive, size, and consolidant is due to its availability, ease of preparation and use, and lack of toxicity. The scientific literature reveals much about funori's relation to other red seaweeds and gives insight as to why it has endured as a reliable material. Our research in the laboratory to find the best methods of preparation revealed that funori is flexible in preparation and applicable to most consolidation treatments that require a low-strength material. In addition to the funorans, our seaweed research examined the agars and carrageenans. Agar, solid at room temperature, is inappropriate for use as a consolidant. Our East Asian painting laboratory has been experimenting with carrageenan with good results, although, unlike funori, with its long history of use in conservation, carrageenan's durability over time is not yet known. Our reasons for investigating funori were to increase its purity, extract as much soluble material as possible, find the most effective and efficient method of preparation, and make a portable product with a long shelf life.
We would like to thank all the companies and people who shared their experiences with funori, in particular Andrew Hare, supervisor of East Asian painting conservation, and John Winter, senior scientist at the Freer Gallery of Art and Arthur M. Sackler Gallery. We are grateful to the Andrew W. Mellon Foundation for its generous support of this research through its funding of the East Asian Paintings Research Program at the Freer Gallery of Art and Arthur M. Sackler Gallery.
SUPPLIERS OF FUNORI
Aiko's Art Materials Import, Inc. 3347 N. Clark St. Chicago, Ill. 60657 phone: (773) 404-5600 fax: (773) 404-5919 e-mail: email@example.com
University Products 517 Main St. P.O. Box 101 Holyoke, Mass. 01040-0101 phone: (800) 628-1912 fax: (800) 532-9281 e-mail: firstname.lastname@example.org
Talas 568 Broadway New York, N.Y. 10012 phone: (212) 219-0770 fax: (212) 219-0735 e-mail: email@example.com
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JOSEPH R. SWIDER earned a BS in chemistry and art history from the University of Rochester in 1991 and a PhD in nuclear chemistry from the University of Maryland at College Park in 1998. During a portion of his graduate studies, he was employed in the Science Department in the National Gallery of Art in Washington, D.C. In 1998 he received a National Research Council postdoctoral fellowship at the National Institute of Standards and Technology in Gaithersburg, Maryland. Following this fellowship, he was employed as a research scientist at the Freer Gallery of Art and Arthur M. Sackler Gallery through a grant from the Andrew W. Mellon Foundation in scientific research of East Asian painting materials. Currently he is a senior research scientist for McCrone Associates, Inc. Address: McCrone Associates, Inc., 850 Pasquinelli Dr., Westmont, Ill. 60559
MARTHA SMITH has a BA in communications from the University of Maryland University College. She is a conservator at the Freer Gallery of Art and Arthur M. Sackler Gallery, caring for Near Eastern, South Asian, and Western works of art on paper. She has been preparing and using funori for more than 20 years. Address: Department of Conservation and Scientific Research, Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution, Washington, D.C. 20560-0707