In the Laboratory
Bridging the Gap: From Traditional Silk Dyeing Chemistry to a Secondary-School Chemistry Project
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M. Fátima Paixão* Escola Superior de Educação, Instituto Politécnico de Castelo Branco, Rua Faria Vasconcelos, 6000-266 Castelo Branco, Portugal; *
[email protected] Mariette M. Pereira Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal António F. Cachapuz Departamento de Didáctica e Tecnologia Educativa, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
This article describes the design and implementation of a project involving Portuguese high-school chemistry teachers and their students (1, 2). However, it is not only a Portuguese project, but can also serve for secondary schools or even colleges in similar contexts. It is presented as an example of how local resources can be used to explore the relationships between science, technology, and society (STS). The project incorporates local art, history, and industry into the curriculum, which are relevant to real life, thus making chemistry more meaningful to students. The argument is in line with the STS approach to chemistry teaching at all levels. This educational perspective focuses on the impact of science and technology on society and of society upon science and technology, which are of increasing importance and creates new demands on citizens for insights and understanding (3). STS approach guarantees opportunities for students to correlate science with social, technological, cultural, economical, environmental, and historical dimensions, among others. These are aspects that configure real science (4, 5). At the same time it encourages a teaching perspective that considers stimulating informal learning contexts, such as museums, factories, and the city.
(Iris spp.), walnuts (Juglans regia L.), chamomiles (Chamomilla recutita L. Rauschert), onions (Allium cepa L.), and madder roots (Rubia tinctorium L.). Some additional natural products used as dyes originated in Brazil and India, such as saffron (Crocus sativus L.), sandalwood (Santalum album L.), catchu (Castilloa elastica. Cerv.), indigo (Indigofera tinctoria), Brazilian wood (Haematoxylon campechianum L.), pastel (Isatis tinctoria L.), and tea leaves (Camellia sinensis L.), among others. In the ancient coverlets and other original pieces, these extracts were the main dyes used in the silk dyeing process. The museum of Castelo Branco presents a permanent embroidery exhibition including a set of samples of natural dyeing materials from both plants and animals. In the museum embroidery workshop traditional natural dyes are still prepared to repair old coverlets from the museum collection or from individuals.
Project Goals The central goals of our project were to explore formal and informal learning contexts to (i) explore in a large and meaningful context, the experimental work related to silk dye chemistry and establish relationships between science, technology, society, and culture; (ii) develop a better understanding of the chemistry involved in dyeing processes including the use of laboratory techniques to extract natural dyes and to prepare synthetic dyes; and (iii) promote new relationships between the schools and the local community through links between formal and informal contexts. Background In Portugal we can find fine, unique, and colorful traditional embroidery that is made of silk on linen (Figure 1). These art works have cultural and economic dimensions related to the city of Castelo Branco and are influenced by eastern coverlets from the 17th century. Many autochthon species containing coloring pigments have been extracted and used as dyes for silk, such as lilies 1546
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Figure 1. Castelo Branco embroidery—an ancient coverlet.
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In the Laboratory
The project involved the participation of three chemistry teachers and their students, near sixty 12th grade (17year-old) students from three Portuguese secondary schools of the region of Castelo Branco and comprised three phases: (i) project contextualization, (ii) experimental development, and (iii) enlargement of the learning context (STS interrelations). The first phase focused on the contextualization of the experimental development of the overall project. It started with a visit to the museum of Castelo Branco and its coverlets exhibition and workshop. The visit included lectures and activities led by the embroiderers and museum staff about historical and actual dyeing processes and artistic, cultural, and economical aspects. After the visit, the students found natural autochthonous dyeing species from the countryside that were used in the second phase—the laboratory activities. Broadly speaking, in this first step the students were engaged in searching for natural dyes, learning about the dyeing processes, and relating them to the traditional dyeing processes. This established the interrelations between chemistry and other domains such as biology (looking for botanical categorization of the vegetal species), culture (a different understanding of a museum), and arts and techniques (the
meaning of colors and the symbolism of coverlet motifs and also ancient dyeing processes). The students were required to prepare posters describing their searching activities and preliminary background information regarding the uses of the materials collected. Students were allowed a week to work on the poster. Their posters were presented to the scholar community and constituted an evaluation element. The second phase was experimental work involving several laboratory techniques. In each of the three schools, the students were divided in groups of four or five, each one performing the experimental procedures. The task took nearly six hours, divided into two or three equal sessions. Students took part in several laboratory techniques involving natural dye extraction from plants, total synthesis, and the use of mordants to obtain a variety of colors (Figure 2). Connections with fine arts were also made when the students used the results of their experiments to make colored silk threads (Figure 3) and handcrafted kerchiefs. A set of experimental protocols was prepared or adapted by the authors in collaboration with the secondary school teachers involved in the project (8–10). Each protocol included the chemical structure of the substances, a piece of history that makes the chemical context more significant, the experimental procedure, and a set of questions allowing a general discussion. Selected examples of the experimental protocols are presented in the Supplemental Material.W The chemistry processes involved did not require sophisticated apparatus and all of the materials were inexpensive. At the end of each experimental session, the students presented and discussed the results with the class. The postlaboratory questions induced a rich discussion, permitting the evaluation of the level of understanding of the chemical concepts. The students obtained silk threads and handpainted kerchiefs that were well appreciated. The third phase consisted of different activities aiming at a deeper understanding of STS interrelations. The teachers and their students visited several research groups of the Chemistry Department at the University of Coimbra (a nearby town). During one full-day visit, the students were exposed to different experimental research activities. Furthermore, they participated in the classic synthesis of alizarin, a landmark of dye chemistry (9) that requires special highpressure equipment not accessible in the secondary schools. They also used an UV–vis spectrophotometer to measure the
Figure 2. Students extracting natural dyes.
Figure 3. The use of mordants to obtain a large variety of colors on silk threads.
Nowadays, the chemical industry dominates the dye process, and the great majority of beautiful colors that are used on embroideries are synthetic dyes, some of them with the same molecular structure as the natural ones, but now obtained by total synthetic chemical processes (6, 7). Although dyeing no longer exists as a traditional art in most parts of the world, museums often employ professionals who are aware of traditional techniques. The museum of Castelo Branco employs an embroiderer who prepares beautiful colors for silk dyeing using natural dyes made with ancestral techniques passed from one generation to another. In the museum’s embroidery workshop, ancestral techniques exist together with modern industrial synthetic dyeing processes. This constitutes a rich heritage that is both local and national and cultural and economical. Joining together such apparently broad aspects, that at the same time connect school activities with social and technological aspects, allows students and teachers to go beyond chemistry solely as an academic subject (3–5). The Design and Development of the Project
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In the Laboratory
absorption spectra of water solutions of alizarin and their colored solutions resulting from the addition of metal salts, such as iron(II) sulfate, aluminium(III) sulfate, and chromium(II) sulfate, the mordants used in the silk dyeing process. The students recorded the absorbance and the transmittance spectra of the different colored substances. A useful discussion about the structure of the compounds and the fundamentals of absorption spectroscopy improved the understanding of the relation between the spectra and the observed colors. The students’ understanding was successfully tested when they identified an “unknown” substance from the corresponding absorption spectrum. All these aspects are directly related with the 12th Secondary Chemistry Portuguese National Curriculum. Students expressed both in the laboratory and in written reports, the relevance of the visit for their general understanding of such concepts. To further explore the relation between science and technology, students and their teachers also visited a local textile industry with large-scale dyeing processes. This visit was oriented toward improving the students’ understanding of industrial processes. They gained an understanding of the relevance of research and quality-control laboratories inside the factory, as well as the existence of big machines producing large quantities of threads and woven material from natural and synthetic fibres. They observed the dyeing process actually used to color the skeins of silk used in the embroidery of Castelo Branco. The visit also precipitated an important environmental discussion involving the treatment of local water effluents as a result of industrial production. A final aspect of the project was the visit to the Textile Museum of Covilhã (another nearby town). This is a museum with a rich archaeological industrial heritage. It was rebuilt on the ruins of an ancient factory of the 18th century where dyes and dyeing processes had special evidence. This historical approach allowed the students to obtain a different image of science and of the construction of scientific knowledge by the perception of possible interrelations between science, technology, and society in ancient periods. All visits were carefully prepared in advance. At the end each student was asked to present a short written report including an evaluation about this way of learning chemistry. The reports were also used as assessment elements. All the students said that this project contributed to the growth of their chemical knowledge and some of them suggested that the involvement in this kind of project increased their interest in future chemistry careers.
Juglone Synthesis Concentrated sulfuric acid (2 mL) was added to sodium dichromate (0.5 g) dissolved in water (2 mL). To this mixture 1,5-dihydroxynaphthalene (100 mg) was added. The mixture was then heated for 30 minutes. After the mixture cooled to room temperature, the aqueous solution was extracted twice with dichloromethane (25 mL), dried, and the solvent evaporated to isolate juglone (Figure 4).
OH O OH OH red OHⴚ
OH O OH O purple Scheme I. pH dependence of the isolated dye (flowers of lilies).
O
O
Figure 4. Structure of juglone.
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General Procedure for Natural Dye Extraction The extraction of natural dyes from the plants were done according to literature procedures (8) using the appropriate solvents, water or ethanol (70 ⬚C), for 45 min. The isolated dye was dissolved in water (10 mL) and divided into small test tubes. Small quantities of NaOH (2 g in 100 mL of water) or HCl (4 mL of 36% HCl in 100 mL of water) were added to the dye solution. The different colors obtained at different pHs were recorded and interpreted (Scheme I).
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OH
N
N
Scheme II. The azo-dyes have been synthesized from arene diazonium salts with different phenols or naphthols (10).
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Mordants and Dyeing Processes
The azo-dyes were synthesized according to previously described procedure (10) from arene diazonium salts with different phenols or naphthols (Scheme II). If the local regulations do not allow the use of some of the proposed reactants in schools or if the laboratory hoods are not well ventilated we recommend the acquisition of commercial dyes, such as alizarin or juglone, to be used with mordants in these dyeing processes.
the project served as a basis for several useful chemical discussions about some topics of the Chemistry National School Curriculum (12th grade) such as acid–base equilibrium, structure and reactivity, intermolecular forces, solubility, and general fundamentals of absorption spectroscopy. Furthermore, this project allowed fruitful partnerships between secondary schools and other institutions, such as the university, museums, and industry. As a rule, few students in Portugal have access to such opportunities to experience rich learning situations. It would be interesting to investigate whether these kind of formal and informal learning contexts become incentives to follow scientific careers. The strategy followed does not aim at any kind of generalization. We simply present it as an example of exploring STS interrelations to motivate the students for the chemistry learning. Furthermore, the experimental protocols presented above can be used in different teaching situations in contexts involving dyes and dyeing processes.
Hazards
Acknowledgments
All reagents should be handled in a well-ventilated hood with students wearing gloves, safety glasses, and lab coats. Ethanol is highly flammable. With phenol, naphthol, 4-nitroaniline, and sodium nitrite, prevent skin and eye contact. They are toxic and harmful by inhalation and absorption by skin. Sodium nitrite is a strong oxidizing agent. It should be handled in a well-ventilated hood. Phenol and naphthol are poisons that may be absorbed through skin. Concentrated solutions of HCl and NaOH are corrosive to eyes, skin, and mucous membranes. They can cause irreversible damage. Dichloromethane is a suspected carcinogen and can cause serious damage to health by prolonged exposure through inhalation.
The authors would like to thank the three secondaryschool teachers who implemented this project and all the institutions that welcome the project. The authors also thank the Portuguese Foundation for Science and Technology, FCT, Ciência Viva PIV-1915, for financial support.
Concluding Remarks
1. Cachapuz, A. (coordinator) Ciência Viva Project. 2001, FCT, PIV-1915. 2. Paixão, M. F.; Pereira, M. M.; Cachapuz, A. 6th ECRICE [CDROM]; University of Aveiro-Portugal, 2001. 3. Millar, R. Sch. Sci. Rev. 1996, 77, 23–32. 4. Cross, R. The Austral. Sci. Teach. J. 1990, 36, 33–38. 5. Fensham, P.; Wynne, H. Internat. J. Sci. Educ. 1999, 21, 755– 763. 6. Travis, A. S. The Rainbow Makers. The Origins of the Synthetic Dyestuffs Industry in Western Europe; Lehigh University Press: Bethlehem, PA, 1993. 7. Delamore, F.; Guineau, B. Colors: The Story of Dyes and Pigments; Discoveries, Harry N. Abrams, Inc. Publishers: New York, 2000. 8. Stick, R. V.; Mocerino, M.; Franz, D. A. J. Chem. Educ. 1996, 73, 540–541. 9. Brown, T. M.; Cooksey, C. J.; Dronsfield, A. T. Educ. Chem. 1999, 36, 20–22. 10. Harwood, L. M.; Moody, C. J.; Percy, J. M. Experimental Organic Chemistry, Standard and Microscale, 2nd ed.; Blackwell Science Ltd: Oxford, 1998; p 612.
The silk dyeing procedure using mordanted natural, synthetic, or commercial dyes, with iron(II) sulfate, aluminum(III) sulfate, and chromium(III) sulfate were carried out using literature methods (9). A wide range of colored silk threads was obtained. The different colors were recorded and interpreted.
Azo-Dye Synthesis
The project worked well as a means of exposing the students to a wide variety of different interrelated activities in both formal and informal contexts. It received positive evaluation from the teachers and students. Most comments by the students indicated that they enjoyed the work: The synthetic dyes mimic the colors and shades of the embroideries from the 17th and 18th centuries perfectly. It is very interesting to isolate the dyes and to do the spectroscopic analysis. We get a better understanding of all these aspects. This work was very important for us; it was not just the academic topics but essentially their integration with cultural and social roots.
This project emphasizes how chemistry concepts may be used for a better understanding of local and daily life. This kind of project allows students and teachers to go beyond chemistry solely as an academic subject. At the same time,
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Supplemental Material
Selected examples of the experimental protocols are available in this issue of JCE Online. Literature Cited
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