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Alternative Material - Funori as Consolidant for Powdery, Matt Paint on Ceramics and Stone

Author: Julia Wagner.


This experiment explored the use of Funori as consolidant for powdery, matt paint on ceramics and stone as an alternative consolidation material (i.e. non-detrimental to the environment and non-toxic for conservators). The red seaweed found along the coast of Japan has a long history of use in Asia and has also been used in Europe since around the 1950s for certain specialisations such as paper, paintings and conservation of some objects. While tried and tested as a consolidant, cleaning agent and/ or light adhesive for some specialisations, not much literature was found for ceramics and stone. So this experiment was conducted in order to become more familiar with this material and in particular, test its properties and compatibilities with the medium of ceramic and stone. Preliminary research garnered some awareness on the use of Funori in the treatment of a stone bodhisattva at the Freer Gallery of Art and on the use of Funori for the production of unbaked clay statues in Japan during the Nara period (AD 710 to 794). This may indicate that this material could be compatible with the medium of ceramics and stone.

Source: https://tri-funori.com (left and right), Françoise Michel (middle).

About funori

Funori is a polysaccharide that consists of galactose units containing a fairly high proportion of sulphate. Apart from the sulphate, it is chemically similar to agar. Viscosity and surface tension are low when warmed up, enabling more efficient penetration of porous surfaces. The ability to build a large number of hydrogen bonds means it can bond a large amount of water and hence avoid the creation of tide lines around the treated area.

Source: https://dictionary.goo.ne.jp (left), Jillian Harrold and Zofia Wyszomirska-Noga (right).

About Production and Preparaton

After harvesting, the seaweed is rinsed and dried in the sun on straw mats and in order to aid the bleaching process, water is repeatedly sprinkled over it. At a later stage, the Funori mats are stacked until dried completely and sold, either rolled or cut into squares. Depending on the supplier there may be chemical bleaching with sodium peroxide or a natrum hydroxyl solution involved in the process.

Source: tri-funori.com. Preparation of seaweed without chemical bleaching.


A recipe to prepare the consolidant to a solution of 0.5% (w:w) Funori in de-ionised water and isopropyl alcohol (5%) was adapted from several sources. Isopropyl alcohol was added for longevity (optional).

Source: own. Preparation of Funori solution from left to right.

Samples of various porous substrates were painted with chalk (no binding medium other than tap water). The bottom half of the 2x3cm rectangles was consolidated with a hake brush through a sheet of Japanese paper. The L (black/white), a (red/green) and b (yellow/blue) values of the unconsolidated and consolidated areas were measured with a colour spectrophotometer (Konica Minolta CM-2600d). The type of colour change was calculated (difference between unconsolidated and consolidated L, a, and b values: △L, △a, △b) as well as the extent of colour change.

Source: own. Samples painted with chalk, bottom half consolidated, from left to right: Limestone A, Limestone B, plaster, high- and low-fired earthenware and unbaked clay.

Results, Discussions and Conclusions

△L: Slight darkening (especially in limestone B) in general to be expected in consolidation.

△a: Slight reddening (especially in unbaked clay) to be expected given the colour intrinsic to Funori.

△b: Slight yellowing (especially in unbaked clay) to be expected given the colour intrinsic to Funori.

△E: Overall extent of colour change within acceptable range of 0.0 to 1.0 with the exception of limestone B due to the slightly more apparent darkness of the consolidated area.

No tide lines were observed in this experiment.

E Interpretation

0.0 – 0.5 No difference to almost no difference

0.5 – 1.0 Difference can be perceived by the trained eye

1.0 – 2.0 Minor colour difference

2.0 – 4.0 Obvious colour difference

4.0 – 5.0 Significant colour difference that is rarely tolerated

> 5.0 The difference is evaluated as a different colour

In conclusion the results of this experiment were promising and research into other documented experiments conducted with Funori also showed:

- pH neutrality and a low risk of mould growth

- good stability as a consolidant of matt powdery paint.

- good aging properties in accelerated UV-aging test.

- similar results in terms of minimal colour change to consolidated areas.

Formation of a precipitate on salt contaminated surfaces however, was observed by Catenazzi (2017) and further investigation is needed before concluding Funori’s compatibility with ceramics and stone. Another possibility for further research is the testing of its stability as a light adhesive and perhaps improving this by changing the extraction temperature.

Things to keep in mind when working with Funori:

- Preparation of Funori is comparatively time consuming

- It has a long shelf-life in the dried state but once prepared it can expire within days

Quicker preparation times and increased longevity could be achieved via the use of JunFunori (Lascaux) or TriFunori (TriFunori™). These are proprietary preparations of Funori processed to minimise user preparation time as well as reduce variations in starch content and pH, as should be expected from a natural material.

Overall, Funori is potentially a sustainable product with many useful properties that may be maximised by varying the preparation and application methods.


Michiel Overhoff, Kate van Lookeren Campagne, Freer Gallery of Art, University of Amsterdam, Zoë Bedford and Jamilla Peeters.

Selected bibliography

Catenazzi, Karin, “Evaluation of the use of Funori for consolidation of powdering paint layers in wall paintings”, Studies in Conservation, Vol. 62, Issue 2, 2017.

Geiger, Thomas and Françoise Michel, “Studies on the Polysaccharide JunFunori Used to Consolidate Matt Paint”, Studies in Conservation, Volume 50, Issue 3, 2005.

Harrold, Jillian and Zofia Wyszomirska-Noga, “Funori: The use of a traditional Japanese adhesive in the preservation and conservation treatment of Western objects”, Adapt & Evolve 2015: East Asian Materials and Techniques in Western Conservation. Proceedings from the International Conference of the Icon Book & Paper Group, London 8–10 April 2015.

Hayakawa Noriko, et al., “Characterisation of funori as a conservation material: Influence of seaweed species and extraction temperature”, Studies in Conservation, Vol. 59, sup 1, 2014.

Kariya Hiroko, “The use of Funori as a consolidant on matte paint layers: the conservation of a monumental polychrome sandstone Bodhisattva”, Abstracts of papers presented at the twenty-third annual meeting, St. Paul Minnesota, June 4-11, AIC, 1995.

Konica Minolta, Precise colour communication. Colour Control from Perception to Instrumentation.

www.konicaminolta.eu/en/measuring-instruments/learning-centre/colour-measurement/precise-colourcommunication.html, accessed 15-03-2018.

Michel, Françoise, "Funori and JunFunori: Two Related Consolidants With Surprising Properties", Proceedings of Symposium 2011: Adhesives and Consolidants for Conservation: Research and Applications, October 17-21, 2011.

Michel, Françoise et al., “Funori, ein japanisches Festigungsmittel für matte Malerei“, Zeitschrift für Kunsttechnologie und Konservierung Jahrgang 16, Heft 2.

Masson, Oliver & Michaela Ritter, “Fräulein Huth’ and the red seaweed: Consolidation of a collage by Kurt Schwitters with JunFunori®”, The Paper Conservator, Vol. 28, Issue 1, 2004.

Moran, Sherwood F., “Structural Features of Clay Sculpture of the Nara Period”, Artibus Asiae, Vol. 23, Issue1, 1960.

Swider, R. Joseph & Martha Smith, “Funori: Overview of a 300-year-old consolidant”, Journal of the American Institute for Conservation JAIC, Vol. 44, Nr. 2, Article 5, 2005.


tri-funori.com, accessed 15-03-2018.

Winter, John, “Natural adhesives in East Asian paintings”, Studies in Conservation, Vol. 29, sup 1, 1984.

Yamasaki K. and Nishikawa K., “Polychromed Sculptures in Japan”, Studies in Conservation, Vol. 15, Issue 4, 1970.

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