By Saiful Bakhri
Indonesia, like many other economically developing countries, faces a wide range of conservation challenges from education and skill gaps to natural disasters and climate conditions. In regard to the latter, with relative humidity ranges between 70 and 90%, Indonesia’s cultural heritage is constantly threatened by biodeterioration. Heritage buildings are often infested with agents of biodeterioration like mosses and lichens.
To cope with this, the Borobudur Conservation Office (BCO), as the country’s agency responsible for conservation research and development, has developed a range of methods for removing this biodeterioration.
From the late 1990s to the 2000s, to remove agents of biodeterioration from the stone surface, the BCO used a paste made from a mixture of sodium bicarbonate, carboxymethyl cellulose, Aquamoline (tetrasodium salt) and Arkopal (nonylphenol ethoxylate). While the paste proved to be effective in removing mosses and lichens, some of these products are harmful to humans and the environment. From the 2000s onwards, along with UNESCO’s recommendation, the BCO has been exploring and scientifically investigating safer and more environmentally friendly materials to be used in cultural heritage conservation. BCO have been engaged with traditional communities, academics and local home industries to find plant-based materials and traditional methods that can help them to understand and conserve cultural heritage. Recently, they successfully developed citronella essential oil as an emulsion to remove mosses and lichens from stone surfaces.
There are many ways to produce essential oils, and in Indonesia citronella essential oil is generally produced through steam distillation of citronella (Cymbopogon nardus). As a major exporter of a variety of essential oils products, it is common to find traditional essential oils steam distillation facilities in Java and Bali. Therefore, essential oils are less expensive and more accessible for Indonesians.
How does it work?
Every 100 ml of Citronella essential oil is emulsified into one litre of distilled water with 50 ml of Tween 80 (Polysorbate 80) surfactant. The oil is first mixed with the surfactant, creating a milky white solution, and then the distilled water is added. The prepared solution is poured into a spray bottle. A handheld pump pressurised spray bottle (click here to see the model used for this treatment) can be used to cover an outdoor surface in a location with limited access to electricity. The BCO recorded that every 900 ml of solution can cover one square metre of stone surface.
To apply, spray the solution directly, with reasonable distance, to the moss and/or lichen infested stone surface. In approximately 24 hours, the agents of biodeterioration will turn brownish indicating that they have died. Then, they can easily be removed with a small bundle of dried coconut fronds (sapu lidi), akin to stiff broom bristles. This tool is inexpensive and can easily be found in tropical Southeast Asia. The tool is used in this case because it is hard enough to scrape off the growth, but soft enough to not scratch the stone. Lastly, the surface must be rinsed with clean water to remove any remaining emulsion or biological growth residues.
This method is deemed to last for a year, and is safe for both the conservator and the environment. Last year I had the chance to join the BCO’s online course called BIOCHEMCO’ 20 where I gained information on the use of citronella essential oil. Earlier this year my colleagues and I at the Bali Cultural Heritage Preservation Office managed to test this method on a stone structure inside the Canggi Hindu Temple, Gianyar, Bali. We recreated the preparation
and application method that had been presented, and it was wonderful to see for ourselves how much easier it was to remove the mosses and lichens once they were dead. We applied this method on 24 February 2021, and I am still continuously monitoring, bi-weekly, the long-term effect of this method on the structure. So far, the biological growth has not returned.
On 9 April 2021, the Director-General of Culture of the Republic of Indonesia, Hilmar Farid, was invited to Central Java for a ceremony. It was a ceremony to hand over the intellectual property rights of the use of citronella essential oil to remove biodeterioration from stone cultural heritage surfaces, initiated by the BCO to the Ministry of Education, Culture, Research and Technology of the Republic of Indonesia. The ceremony was held to celebrate the achievement of the BCO scientists, along with other involved stakeholders, marking their contribution in inventing this sustainable conservation material and method. To show their gratitude towards the state facilities, the BCO gave the intellectual property rights for this technique to the state. This ceremony, published on social media, is a way to encourage small-to-medium scale essential oil industries to keep producing, because the demand will eventually increase as more government agencies and the wider public begin to use this new product.
The BCO is currently developing other plant-based materials to be used in the care of other types of cultural heritage. I am sure that the exploration, research and development of alternative environmentally friendly conservation materials is one of the answers to promoting sustainable conservation practices.
Saiful Bakhri is an emerging conservator at Bali Cultural Heritage Preservation Office, Gianyar, under the auspices of the Directorate General of Culture, Ministry of Education and Culture of the Republic of Indonesia. He is also a conservation consultant for Museum Pustaka Lontar, Karangasem. Having completed his master’s degree in cultural materials conservation at the University of Melbourne, Saiful’s expertise lies in the areas of place-based conservation and disaster management for heritage sites and museums.
(Read the article and watch the treatment video in the August-September 2021 "News in Conservation" Issue 85, p. 12-15)