Discovery

Natural Dyeing

Dr Owen J. Curnow

Join in the International Chemistry Celebration 1999 and National Chemistry Week (11-17 September) with two experiments to investigate the extraction of natural dyes and their use in the dyeing of fabrics.

We publish the first experiment here to get you started on testing natural dyes. Check out the brochure A World of Colour available on the International Chemistry Celebration Web pages (http://www.chemcenter.org/ichc or http://www.acs.org/memgen/meetings/ichc/ichc.htm) or at the National Chemistry Week Web pages (http://www.chem.canterbury.ac.nz/ichc.htm).

The brochure details the two experiments being used in the International Chemistry Celebration. You can take part by contributing to the international database on indigenous dyes, by submitting your dyed fabrics for incorporation into a Global Collage, or by entering the competition to design a new national flag using the natural dyes that you discover. See the Web pages for entry forms and additional information.

Plant Rubbing

(Experiment 1 from A World of Color)

Here's a chance to identify natural sources for eight colours: red, orange, yellow, green, blue, violet, brown & black, and to investigate how colours may be changed chemically.

Supplies:

• plant materials (e.g. flowers, leaves, grasses, roots, bark and berries)
• several pieces of coarse white paper
• 100 ml (1/2 cup) distilled white vinegar (household vinegar)
• 5 g (1 tsp) baking soda (sodium hydrogen carbonate)
• 100 ml (1/2 cup) distilled water or rainwater
• several tissues or cotton swabs

Procedure:

1. Collect plant samples from near your home. (A small sample -- such as one leaf or several berries -- is sufficient.) Do not take bark from a live tree. Ask an adult before picking samples from unknown plants. Never taste the samples, and always ask permission beforehand.

2. Rub a 75 mm streak of each plant sample onto a piece of coarse white paper. Record in a notebook the colour, or lack of colour, that is transferred to the paper. Indicate which part of the plant you tested (e.g., leaves, root, or stem). Try other parts of the same plant, as colours may come from unexpected sources.

3. Test as many sources as possible. Identify a source for each of the eight colours listed above.

4. Dip a tissue or cotton swab into the vinegar (a mild acid solution), and wipe one end of the streak you made in Step 2. Did the colour change? In what ways? Record these observations.

5. Repeat Step 4 using a mild base solution made by dissolving 5 g of baking soda in 100 ml of distilled water or rainwater. Record your results.

Did you find all eight colours?

Did you find the colours with or without adding acid or base?

Safety Notes

• never use any cooking pots, pans or utensils for these experiments
• never leave the experiment unattended
• always consult with your adult supervisor before beginning these experiments
• never touch hazardous materials or taste anything
• wear protective eyewear and clothing when required
• always wash your hands after collecting samples and finishing your experiments

Dr Curnow is in Canterbury University's Chemistry Department.