For a long time, Vietnamese people have used colorant plants and, even now, they remain a part of daily life. However, at this time, there is no document or evidence precisely recording and describing the appearance of these plants. Via modern evidence, in the two wars in Vietnam (the resistance against French Colonist and the war against America), the symbol of this period was the farmers in brown or black clothes and the soldiers in green uniform. These colors helped them to disguise and hide from their enemies. Everyone wore dark-colored clothes to avoid enemy planes and for easy hiding [1]. If a shirt was white, it was dyed moss green or a waning-grass brown called “màu phòng không” (literally, air-defense color) (Tình 2010) using Trau leaf (Piper betel) or Bang leaf (Terminalia catappa). Traditional clothes and colors have been part of festivals and worshipping ceremonies for ages. The King Hung legend mentions Chung cake wrapped in La dongleaves (Phrynium spp.) as green represents earth and Day cake made of sticky rice as white represents heaven. Prince Lang Lieu created these two types of cake, which he submitted for the contest to determine the heir to the throne. Thanks to his unique idea, Lang Lieu became the next Viet King. Colorant plants have always travelled along side the history and development of every ethnic group in Vietnam (Pháp 1968, Schultz 1965). However, the persistence of plant-derived dyes and asociated cultural practices and traditional knowledge is threatened with rapid socio-economic change in Vietnam. Research is needed to document the ethnobotany of dye plants in indigenous communities and associated traditional knowledge towards cultural conservation.

The study in this paper is based on real-life interviews and field investigations completed in the communities of ethnic minorities in some provinces in Northern Vietnam. Field investigations and sample collecting were undertaken in chosen areas from 2009 to 2011.

Study site: We focus on high-density ethnic minorities areas such as, black Tai people in the Son La Province and Dien Bien Province; H’Mong people, Dao people, Tay-Nung people and Giay people in the Lao Cai Province and the Cao Bang Province [2]. Undertaken at twelve mountainous hamlets and villages of ethnic minorities as listed below: Tay-Nung people: Den hamlet (Sapa commune, Lao Cai Province); Lung Quang hamlet (Thong Nong commune, Cao Bang Province).

Giay people: Lau hamlet (Sapa commune, Lao Cai Province) as shown in Figures 1 and 2.

Figure 1: Khâu út cake (steamed rice cake), the traditional cake of Giay people in Muong Khuong Commune,Sapa, Lao Cai.

Figure 2: Traditional dishes of Giáy people in Tet holiday, in L?u village.

Thai people: black Thai in Bo, Nhop, Bia and Bang hamlets (Thuan Chau commune, Son La Province); Phang-3 hamlets (Muong Phang commune, Dien Bien Province); white Thai in the Na Muoi hamlet (Moc Chau commune, Son La Province). H’Mong, Dao people: Khoang hamlet (Muong Khuong commune, Lao Cai Province); Ranh and Du hamlets (Da Bac commune, Hoa Binh Province) as shown in Figures 3 and 4.

Figure 3: Seven-colored steamed, sticky rice, made by Nung people at Muong Khuong, Sapa, Lao Cai.

Figure 4: Colorful steamed sticky rice of Dao people in Lao Cai.

Field research: A Data-base was collected through participant observation and semi-structured interviews (Gary Martin, 2002) with open questions regarding the local knowledge on using colorant plants. The questions are related to dye plants and dye technique [3]. Key informants were identified on the basis of semistructure interviews for transect walks through the surrounding mountains and fields to collect documented dye plants for samples and voucher specimens. Picture cards with dye plants were shown to informants to document local knowledge of dye plants. Research samples: Scientific names have been identified according to the Flora of Vietnam (FV). The samples are being preserved in the Hanoi Herbarium of the Institute of Ecology and Biological Resources and Vietnam National Museum of Nature.

Checklist of colorant plants

Following survey results, we recorded fourty three colorant plant species for coloring food and beverages. Ethnic people use plants for dyeing and mordanting. A total of ten species are used for red color, seventeen species for yellow, ten species for green, eight for black and four species for purple, one species for blue and one species for orange [4]. Among dye plants that are well known, Peristrophe bivalvis has got several varieties for different colors. Almost research areas, we have recorded purple and pink races, particularly we have met red varieties of P. bivalvis in a few places (Hoa Binh, Son La, Lao Cai provinces); yellow varieties is unique found in communities of Dao (Sapa) and Tay (Muong Khuong) at Laocai province. Checklist is detailed in Table 1 belowing here.

Table 1: Checklist of natural colorant plants for food that used by ethnic people in Northern Vietnam.

Food coloring

Processing experience depending on available materials, the people there have particular methods of collecting and processing pigments [5]. The major methods are hot extracting (boiling ingredients in water to extract colors), cold extracting, solvent extracting, and mixing colored ingredients directly into food.

Hot water extracting method: With this method, the material is boiled in water for 15-20 minutes. Meanwhile pigments in the material dissolve [6]. The extract is used to dye materials before processing food (rice is soaked before making steamed sticky rice, flour is dyed before baking) (Figure 5).

Figure 5: Rice is soaked in Mat Mong extraction for making yellow.

Cold water extracting method: Fresh raw materials are pounded, strained, and soaked with rice in order to create color; then this rice will be used to make steamed sticky rice or pie with the extracted colors. Cold extraction is applied to the materials collected from such species as pine-apple, Rhodomyrtus tomentosa, Basella rubra (Mùng t?i), Reynoutria japonica (C?t khí c?) etc [7].

Solvent extracting method: Since it is used for dyeing food, the solvent to extract color from plants is alcohol. This material is nontoxic, inexpensive and easy to find. The materials containing pigments are cut into pieces or ground, then soaked in alcohol (in the ethnic minority areas the concentration of alcohol is often 35-40%). After a certain time raw pigments dissolve in alcohol and produce a colored solution to dye food [8]. This method is often used to extract color from Morus alba, Eleutherine bulbosa, etc. Pigments extracted by solvents are commonly used in processed beverages (soft drinks, colored wine, etc.)

Use of raw materials directly: Raw materials used for this method are usually leaves of some species (Artemisia spp, Paederia scandens) to create the color of green or ash of some species (Oryza sativa, Rhus chinensis, etc.) to require black color. Figure 6 The Tay and Nung groups in Trang Dinh district (Lang Son) create the color of green by boiling the leaves of Artemisia spp, removing fibers (veins) and crushing into powder, then grinding with sticky rice to make green rice cake. Similarly, the Tay and Nung in Van Quan (Lang Son province) use leaves of Paederia scandens instead of Artemisia spp. (Figure 7). To dye rice cake in black, the Giay and Yao get sticky straw (only straw portion of panicle) burned to ash, then the ash is sifted smooth and mixed with glutinous rice which was soaked overnight, stirred so that the ash stick evenly in rice, then used the mixture to make black glutinous rice cakes [9]. Meanwhile, the Tay and Nung groups (Muong Khuong district, Lao Cai province) use ash of Mu?i tree (R. chinensis) to dye cake black.

Figure 6: Black Chung cake is made by Tay group in Cao Bang Province, Chirita speciosa.

Figure 7: Nh? ngài cake, colored using Artermisia vulgaris. Tay traditional cake used during the 3 March festival (slan ma or the grave visit festival) in the province of Cao Bang.

Unique techniques of creating colors: Ethnic minorities have unique experience of creating different colors in food processing. Here are some experiences in common use,

Changing pH: Taking advantage of a modified color pigments in the material according to pH of the extract, the ethnic minorities have used pickles water (low acidic, pH) and lime water (high alkaline, pH) to correct the colors of extracts [10]. Extracts from fresh turmeric (C. longa) if used to dye immediately would create yellow, if added pickles water (low pH) the extract environment would switch to acid and make orange, if added lime water (high pH) the extract would turn yellow green to dye food. This experience is used commonly among the Tay, Nung, Giay, etc.

Creating different colors from one species: With their unique experience, from the same material with different processing methods, the ethnic minorities can create different colors to dye food. This is the experience we noted when investigating at Nung ethnic groups in Muong Khuong district, Lao Cai province [11]. From the leaves of P. bivalvis (C?m, Ch?m lai) which varietas often make purple, if fresh leaves are pounded with cold water and filtered out of residue a black solution will be gained, if fresh leaves are boiled in hot water a lighter purple solution will be collected.

Coordinate the materials: During the coloring process, the Nung (Muong Khuong, Lang Son province) may create unavailable colors by combining these trees to dye during processing. When leaves of Peristrophe bivalvis are boiled in hot water a purple solution will be collected. Besides, extract from fresh leaves of this plant combined with ash from Dalbergia volubilis would create blue [12]. If the combination of three species (P. bivalvis, D. volubilis and B. officinalis) is used, a dying solution of teal will come out by the following steps: soak rice in the extract from flower of B. officinalis to make it yellow, Figure 8 then soak yellow rice in the solution obtained from fresh leaf extract of P. bivalvis added with ash from D. volubilis. Depending on the amount of ash in the extract, we shall get the color with various shades of green. From our point of view, at a certain angle, pH decides colors of the extracts. Here are pH values of some key extracts (Table 2). However, from experience of the people, when the ash is added into Cam leaves extraction, they have to put inch by inch and always try color. On the other hand, the quality of glutinous rice decides partly the showy beauty.

Figure 8: The blooming season of Mat Mong (Buddleja officinalis) is in March.

Table 2: pH of extractions of colorant plants.

Plant-derived dyes persist at the study sites for their important role in dyeing food and traditional costumes. The most prevalent use of documented dye plants is to color food, specifically glutinous rice [13]. The pigments derived from dye plants at the study site including red, blue, black, purple, yellow and brownish red. These dyes are derived from various plant parts including roots, leaves, flower, stems, bark, tuber, and seed-coat. We recorded fourty three plant species that using as traditional colorant plants by ethnic people. Especially, in festivities and weddings, it is essential for ethnic people to have foods and steamed glutinous rice dyed with natural colorants from plants. These foods have special symbolic meanings to each ethnic minority. Colors and dyeing plants once played important roles in the culture of ethnic minority groups. Traditionally, knowledge of dye plants and their processing was transferred from mother to daughters. The elderly in communities have kept this knowledge. The indigenous knowledge in the utilization of colorant plants in ethnic communities is unique and valuable. However, the transmission of knowledge from the old to the young has decreased and impeded by the deaths of the elders, many young people look for jobs outside of their communities [14]. Therefore, it is urgent to collect and systematize this knowledge. In this study, we do not mention that modernization impacts knowledge of the colorants. This issue will be reported in another publication.

The authors acknowledge the financial support from Ronpaku Program, belonging to Japan Society of Promotion Sciences.