The light purple blossoms of Chinese indigo are a stark contrast to the deep, velvety tone its leaves create when mixed with shell ash and banana peels to dye fabric.
This traditional craft coloured everyday life for centuries but has nearly faded in modern times.
Now, Hong Kong students in secondary school laboratories are emulating this dyeing heritage.
Using beeswax, the pupils trace Lunar New Year blessings onto fabric before dipping it into a steaming pot of natural dye made with Chinese indigo, one of the 2,300 plant species native to Hong Kong. Then, they watch as white fabric transforms into rich shades of blue.
Leading the workshop is interdisciplinary artist Benjamin Hao Lap-yan, who specialises in indigo dyeing and sustainable art practices.
“The leftover fermentation water can be used for composting, and the spent leaves can go directly into compost,” he said. “So the whole production process avoids producing waste that contaminates the soil or water sources.”
The classroom experiment is part of an indigo dyeing programme developed by Hao, Kadoorie Farm and Botanic Garden, and three chemistry teachers from Tak Oi Secondary School.
Blending art, ecology and science, “Encountering Indigo: Exploring the Chemistry and Culture of Natural Dye” introduces students to Hong Kong’s native plants and dives into the cultural roots and scientific principles of this sustainable alternative to synthetic dyes.
Last November, Tak Oi Secondary School students visited Kadoorie Farm to harvest Chinese indigo and repotted some plants on their school campus. They later fermented the leaves to create the dyes for their fabrics.
The process involves various scientific concepts, such as oxidation-reduction reactions, pH balance and fermentation, which transform indigo – when mixed with water, shell ash and banana peels – into a thick blue paste.
Kelly Yip Tsz-ching, a 15-year-old Form Three student, appreciated this chance to learn about sustainability.
“Before joining this programme, I thought all dyeing processes use chemicals – I never thought we could use such simple ingredients to dye textiles like this,” she said.
“This is ancient wisdom passed down.”
Made in Hong Kong
Over the past four years, Hao has devoted his research and creative practice to Chinese indigo and its dyeing process.
After learning about indigo dyeing through a previous project, Hao became curious about the city’s native plants and the local history of natural dyeing. That is how he found that Chinese indigo and another plant called wild yam were suitable for colouring fabric.
Centuries ago, indigo dyeing was integral to Hakka village life in Hong Kong, where the plant was cultivated to create blue textiles.
The artist pointed out that this traditional craft also responds to contemporary issues.
“In the past, people created things necessary for daily life in harmony with their environment, using what was naturally available,” Hao said. “In a way, this traditional practice responds to modern problems like fast fashion and pollution caused by industrial dyeing and production.”
But the artist’s personal connection with this craft goes beyond its relevance to sustainability.
“Using local, natural materials is very important to me because every material carries a deep connection and meaning with the land and with the artwork itself,” he said.
“As someone who grew up in Hong Kong, what is our relationship with the land and with our cultural history? So using this native indigo plant is very relevant and meaningful in that context.”
‘Play seriously’
Delton Li Yiu-sing, a programme manager from Kadoorie Farm’s holistic education department, said he hoped for students to step outside the classroom and “play seriously”.
“We’ve designed this programme to have a spirit of playfulness, but in a serious, meaningful way,” Li said.
Li wants indigo dyeing to broaden students’ awareness of sustainability.
“It helps them see that in the past, people didn’t have chemical dyes or factory-style production,” he said.
“When we talk about sustainable development nowadays, it’s really about how we can ... discover alternative ways of doing things.”
This message is communicated to students with an interdisciplinary approach.
“On the one hand, this project has a very artistic and human-centred feel. On the other, it also dives into the hard science: down to the molecules, how the electrons are arranged [and] how reactions happen,” Li said.
Julian Yu Che-kwan, a teacher who helped develop the programme, described Chinese indigo as a “living storybook” with lessons on ecological interdependence.
“It shows students that this indigo plant is actually a host plant for butterflies and helps them understand how all living beings are interconnected,” he said. “It leads them to think about what role humans play in the ecosystem: are we part of it, or are our actions damaging parts of it and severing those vital connections?”
Natasha Tsang, Tak Oi Secondary School‘s principal, believes this programme is valuable because it teaches students about science, sustainability and local culture while actively engaging them “in a process of inquiry”.
“We don’t want to simply give them all the answers,” she explained. “Instead, by letting them experience first-hand through planting and taking care of these plants, they begin to truly feel and value the meaning of life.”
