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Making Colorful Patterns on Paper Dyed with fled Cabbage Juice Chieko Suzuki Department of Education, Shiga University, 2-5-1 Hiratsu, Ohtsu-shi, Shiga, 520 Japan Many people are aware that red cabhage, red onion, and radish skin turn a brighter red in vinegar. Adults and children alike have used red cabhage juice as a colorful indicator of acidity or basicity.' Extracts from these and other plants contain anthocyanin (redblue) andlor flavonol (colorlessl yellow) dyes whose molecular structures and thus colors are pH dependent.2.3 Red cabbage contains high concentrations of both of these kinds of dyes and thus produces a variety of different colors a t different pH values. The specific pH a t which a color change occurs with an anthocyanin or flavonol is dependent upon-the number of hydroxyl hydrogens that have been replaced by methyl groups and on the identity of the sugars i d metal cations to which the molecules are complexed. Examples of the dyes are shown in Figure 1. The activity described here combines the traditional Japanese technique called "orizome" with the chemistry of acid-base indicators. In orizome a piece of white paper is folded in an intricate pattern and each end of the folded paper is dipped in a colored dye. In this activity, the paper is first colored with a botanical dye and dried. The paper is thenfolded, and portions of it are dipped into clear, colorless solutions of acids and bases. The method is described in more detail below. How To Color the Paper (1) If a roll of Japanese "shoji" paper is used, cut i t into pieces about 18 cm wide. Alternatively, use paper towels, paper table napkins, two-ply tissues, or any paper that is white, absorbent, strong when wet, and not too thick. (2) Tear or chop half a red cabbage into small pieces, and put them into a plastic bag. Add enough isopropyl rubhing
an anthocyanin dye Ow
a flavonol dye
a
Colors ol Red Cabbage Dye at Dlfterent pH Values n H 1 2 3 4 5 6 7 8 9 t 0 1 1 1 2 1 3 1 4 color
588
Journal of Chemical Education
pink
purple
blue
green
yellow
Figure 2. Exlraction of dye by rubbing me plastic bag containing pieces of red cabbage leaves and isopropyl rubblng alcohol. alcohol t o soak the cabbage completely. Rub the pieces together as shown in Figure 2. When the rubbing alcohol has been colored by the dye from the red cabbage, cut a corner off the bag, and let the dye solution pour out into a container. I t needs no filterins4 (3) Soak each o f t h e sheets of paper in the dye solution. Dw them in the shade. Dye the papers a second time if they are not a deep purple cdor. ~ athe csheets ~ in an opaque plastic hag, and keep them in a dark and cool place such as the freezer until used. At room temperature, odor may become a problem after several days.
Presented at the Tenth International Conferenceon Chemical Education. Waterloo. ON, Canada, August 1989. Mebane, R. C.: Rybolt, T. R. J. Chem. Ed. 1985, 82, 285. Goto, T. Pmgr. Chem. Natural Products 1987, 52, 113-158. Gipps, J. Chemda: Aust. J. Chem. Educ. 1990, 28.31-33. Appropriate safety procedures should be followed when preparingand using the dye solutions. If an alcohol is usedas the solvent and children help with these steps, they should wear safety goggles and gloves. Alternatively, the dye can be extracted from red cabbage with water by heating or by using a blender or food processor and straining.
'
Figure 1. Examples of plant dyes.
red
Figure 4. How to dip an end of the folded paper Into a solution
F g~re 3. How
to tolo a sheet of paper into a ragdlar sqare. an equ lalera troangle, and a right-angled ~sorcelestriangle.
How To Make the Patterns
(1) Fold a sheet of the dyed paper six or eight times in accordion pleats. Fold i t again into a square, an equilateral triangle, or a right-angled isosceles triangle as shown in Figure 3. (2) Gather a variety of familiar solutions such as lemon juice, white vinegar, window cleaner, soft drinks, or liquid detergent. Prepare water solutions of, for example, baking soda, ashextract, soap or detergent, antacid, or aspirin. Or, if desired, prepare pH 3 and 5 solutions of aqueous HCl and pH 9,11, and 13 solutions of aqueous NaOH.6 (3) Dip one end of the folded paper into one of the solutions and the other into a different solution as shown in Figure 4. Some examples of the patterns on the folded paper are shown in Figure 5.6
Figure 5. Examples ofpalterns on the f o M paper after dipping it in various pH soIutl0nS.
(4) Unfold the paper gently, and set on paper towels to dry. The design will be a colorful indication of the acidity or basicity of the solutions used. Do not let childrendlptheir folded papers into strong aclds, strong bases. concentrated synthetic detergents or other potentially dangerous solutions. Haba. T. Kamisorne: Kokudosha: Tokyo, 1980.
Volume 68
Number 7 July 1991
589
