Since the start of the Garden City campaign in 1967, city designers and landscapers have carefully selected plants and carried out detailed planning to create the tree-lined boulevards we see almost everywhere in Singapore today. At the beginnings of the campaign, a large focus was to bring in aesthetically-pleasing trees (bright flowers, interesting crown shapes etc.) that are also able to grow well in our tropical climate. Tree species with wide crowns were propagated widely along the roads for their abilities to provide shade. Horticulturists were sent all over the world from Africa to South America to look for such candidates with these 'desirable' properties. As a result of such efforts, exotic trees such as the striking Peacock Tree and the African Mahogany were introduced and propagated in Singapore. Native and fast-growing trees like the Angsana and Rain Tree were also planted all over the rapidly industrializing city as well. In the more recent years, there has been a push to grow more native trees in a bid to preserve and promote Singapore's natural heritage, and to consider how roadside plantings could look more 'natural' by forming layers with different plants, enabling more diversity to exist.  
The success and shifting principles of the greening campaign over the decades have created a global 'repository' of plants right in our neighbourhood. Walking around is like traveling between worlds - the showy Peacock Flower tree with bright red flowers and long stamens from Madagascar, the African Tulip with palm-size flowers from the African tropics, and during Singapore's "Sakura" season we see the a pink carpet of Trumpet Tree's flowers, a species introduced from tropical Americas.  
This diversity has been exciting to explore as we 'hunt' for natural colours. Most of the plant material used thus far has been possible with the help of landscaping teams overseeing the parks (they are usually open to us taking some of the prunings), as well as with the help of volunteers at surrounding community gardens. 
We thought we might share a few of the roadside plants that we have used for ink-making so far this post. Here are 3 common plants we have experimented with thus far:
1. Angsana 
Part of Plant used: Bark​​​​​​​
angsana ink

Made with Angsana ink

On the Plant:
From afar, you may recognize the dome-shaped crown and the typical drooping branches of the Angsana (Pterocarpus indicus). During the flowering season, you might find her flowers in yellow blooms, a beautiful contrast against the background of green leaves. Due to her relatively fast growth, she was cultivated as an 'instant tree' right from the start of Singapore's Garden City campaign. At one point, there were even more than 16,000 individuals found around the city! 
Unfortunately, due to a fungal disease that spread southwards from Malacca to Singapore, many of these trees had to be removed. A severe outbreak in the 1980s led to more than 800 infected trees being removed, out of concerns that the weakened trunks would pose safety issues to road users. Today, they are still one of our most common roadside sightings, though many individuals have also been replaced by other less disease-prone trees. 

Angsana Tree. Image credit to MyPaper.

On the Ink:
We have made many different shades of brown before, but the Angsana's colour profile was deeper and richer. The wood chips (waste collected from ArthurZaaro a sustainable furniture company) yielded a nice chocolate brown after the ink extraction process. The addition of the baking soda to the ink gave a redder brown. We have noticed that baking soda tends to have that effect on lots of browns; it could be a chemical reaction with the high level of tannins in the bark. 
2. Mahogany Trees
Part of Plant used: Bark​​​​​​​

Made with Mahogany tree prunings and modifiers. 

On the Plant:
The first time I noticed this tree was because of its unique-looking fruits. You might have also noticed their large, oblong-shaped brown fruit pods that stands protruding into the sky. For this reason they are also given the colloquial name 'sky fruit' by people. Otherwise, the Mahogany tree looks like many other hardwoods; its leaves is of a darker sheen and it can grow up to an impressive height of 30 meters or more.
The seeds have been traditionally used in Southeast Asia for various ailments that include diabetes and hyperlipidemia. However, there are also cases of liver injury suspected to be linked to the ingestion of Mahogany seeds (CNA, 11 Dec 2018). 

Mahogany prunings and fruits from the park.

On the Ink:
Before extracting colour pigments from wood, we usually soak them in water at least for a few days to soften up the fibers and to ease the extraction process. We did that with some Mahogany branches collected from a landscaping team at the Pasir Ris Town Park, and we are so pleased with the brighter red-brown tones that is somehow close to the colour raw sienna. 

Mahogany wood chips. Notice how the middle of the branches are stained red. 

A variety of flavonoids have been isolated from the reddish extract of the heartwood, such as catechin, epicatechin, and a newly-labelled compound called swietemacrophyllanin (Yazaki, 2014), which is probably responsible for the red wood tones. 
3. Blue Butterfly Pea
Part of Plant used: Flowers

The blues are the result of the Blue Pea ink reacting with different modifers. The brown is from the avocado pits.  

On the Plant:
Many would be familiar with the blue butterfly pea plant as a natural food dye in Malay and Peranakan cuisine. It is also a common roadside climber, often basking in the open, sunny areas. Though it probably originated in tropical Asia, it is able to tolerate a wider climate variation, finding itself growing in subtropical zones of the Americas. On closer look, there are at least 2 varieties of the Blue Pea differentiated by the flowers: single-lobed and double-lobed.

Varieties of flowers of Blue Pea plant.

Googling the plant will lead you to lots of articles on her supposed medicinal benefits. A study done by Thai researchers has shown that its extracts contains active compounds that give to antibacterial, anti-diabetic, wound-healing properties amongst others. Other studies have also demonstrated how feeding lab rats plant extracts improved their memory retention and learning (Rai et al., 2001; Rai et al., 2002). Though results seem promising, it is worth noting that such studies are still in the early stage.  
On the Ink:
We have got very different shades of blues from this plant, probably due to the variations in health and growth environment of the individual plants. Despite her name, the blue pea is technically not blue, though it appears very much so. The flowers consist 9 types of anthocyanins, which in combination result in the red-purple-blue hues observed (Terahara et al., 1996). Blue is actually one of the rarest colours to get in Nature, because there are very few natural blue pigments available. Animals or plants that appear that colour are either due to anthocyanins which are closer to purple than blue, and the way light is reflected off the surfaces (structural colour).     
Another Avenue for Horticultural Waste?
As stated on the website of Singapore's national agency for park management (NParks), Singapore generated a total of 400,000 tonnes of horticultural waste in 2019 alone. Out of the total hortiwaste generated, 73% is recycled. Approximately 40% of recycled waste (pruned branches, trunks, and leaves) are sent directly to composting facilities (Tan & Khoo, 2006), where they are first processed into wood chips and then further broken down by microorganisms to form mulch or compost, after which they will be used for greenery maintenance again. Another portion is burnt at biomass power plants for energy. 
Our experimentation with natural inks so far has led us to consider how we can use such waste to create local inks and paints as well. There are hundreds of plants in Southeast Asia that have a history of ink-making in indigenous cultures, and probably many more undocumented. In our brief survey of local common roadside plants, we have documented at least a dozen of them having colour properties, though the degree of light-fastedness (how long the colours last) varies greatly. Colours extracted from barks last much longer than those from flowers and fruits likely to the high amount of tannins in wood extracts. There are also quite a few native plants that tend to be hidden in forested areas rather than paths. We will share more on these 'hidden' plants in a later post.
Thanks for reading! 
References:
1. Reginald B.H. Tan & Hsien H. Khoo. (2006). Impact Assessment of Waste Management Options in Singapore. Journal of the Air & Waste Management Association, 56:3, 244-254.
2. Rai KS, Murthy KD, Karanth KS, Rao MS. (2001). Clitoria ternatea (Linn) root extract treatment during growth spurt period enhances learning and memory in rats. Indian J Physiol Pharmacol, 45(3):305–13. 42. 
3. Rai KS, Murthy KD, Karanth KS, Nalini K, Rao MS, Srinivasan KK. (2002). Clitoria ternatea root extract enhances acetylcholine content in rat hippocampus. Fitoterapia. 73(7-8):685–9.
4. Reports of liver injury after consumption of 'sky fruit': HSA. CNA, 11 December, 2018. 
5. Yazaki, Yoshikazu. (2015). Wood Colors and their Coloring Matters: A Review. Natural product communications. 10. 505-12. 
6. Terahara N, Oda M, Matsui T, Osajima Y, Saito N, Toki K, Honda T. (1996). Five New Anthocyanins, Ternatins A3. B4, B3, B2, and D2 from Clitoria ternatea Flowers. J Nat Prod 59: 139-144.
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