Three colours from the same dye-bath

Student Sheet

In this practical I will be:

• Observing and reporting on the findings from the experiment.
• Comparing, contrasting and grouping different materials based on my results from the experiment
• Using my scientific understanding to explain the results of the experiment.

Introduction:

Whilst washing your linen clothes in the tub, you notice that the dyes from a few items of clothing have begun to run and colour the water. You think nothing of it and continue to wash your clothes. When you pull some of clothing out of the coloured water, you observe that something very interesting has occurred. Like all good science-artists, you decide to investigate further.

Equipment:

• 4 beakers ( 400 cm³) (or 3 beakers (250 cm³))
• 4 disposable plastic pipettes
• Stirring rod
• 4 large watch glasses or Petri dishes
• 1 pair of tongs or tweezers
• 1 pair of scissors
• Access to a top pan balance (if preparing from solid)
• Spatula (if preparing from solid)
• Weighing boat (if preparing from solid)
• Bottle of distilled water
• Thermometer
• Bunsen burner
• Tripod
• Gauze
• Heat proof mat
• String and paper clips, to make a ‘washing line’
• Crocodile clips or clothes pegs 

Wear disposable gloves

The quantities given are for one demonstration.

• Samples of the following fabrics in white: wool, silk, nylon, cotton, polyester, cellulose acetate (‘triacetate’), polyester/cotton mix. About 1 cm² of each fabric or a few cm of thread will be sufficient. 
• 0.05 g of each of the following dyes: 
  • acid blue 40 (low hazard)
  • disperse yellow 7 (irritant, wear safety glasses)
  • direct red 23 (low hazard)
  • or 10 cm³ solutions of each of the dyes ready prepared (per group)
• A little dilute hydrochloric acid (0.1 M)
• Sodium chloride (if carrying out the extension activity) (low hazard)
• Alum (if carrying out the extension activity) (low hazard)

Method:

1. Cut four strips of each material (about 1 cm x 1 cm is suitable). 1 cm² is enough for groups to use. Larger pieces for a demonstration.
2. Each fabric should be easily identifiable in some way for example by cutting different shapes.
3. Weigh out two samples of 0.02 g of each of the red and yellow dyes and two samples of 0.03 g of the blue dye.
4. Dissolve 0.02 g of each of the red and yellow dyes and 0.03 g of the blue dye in 200 cm³ of distilled water. Or add 1 pipette of each dye (approx. 2-2.5 cm³) to 200 cm³ of water.
5. Add a few drops of dilute hydrochloric acid, stir, and heat to boiling.
6. Place a sample of cotton, cellulose acetate and either wool, silk or nylon in the dye bath.
7. Simmer gently for about ten minutes.
8. Remove the fabrics with tweezers or tongs.
9. Rinse the clothes under running water.
10. Try other materials as well if desired.

Going further:

Mixed dye-baths that produce different colours to the ones suggested here can be devised using the principles governing what dyes colour each of the fabrics described above.

Examine the effect of the dyes individually. 

1. Make three separate dye baths, the first containing 0.02 g of red dye in 200 cm³ of water. Or 1 pipette of dye in 200 cm³ of water in a beaker.
2. The second containing 0.02 g of the yellow dye in 200 cm³ of water. Or 1 pipette of dye in 200 cm³ of water in a beaker.
3. The third containing 0.03 g of the blue dye in 200 cm³ of water. Or 1 pipette of dye in 200 cm³ of water in a beaker.
4. Add a couple of drops of hydrochloric acid to each dye bath.
5. Place a sample of each fabric in each dye bath and treat as before, ie simmer for ten minutes.
6. Remove the samples with tweezers or tongs and rinse.

• Do mordants such as salt or alum have any effect?
• Does pH have any effect?
• Does the time in the dye bath or the temperature of the dye bath have any effect?
• How fast are the dyes to a variety of treatments?

Theory:

Different dyes bond to fabrics in different ways.

Cotton will be dyed red, acetate yellow and wool, silk or nylon blue-green. Some of the yellow direct dye will take to these materials as well as the blue acid dye. 

Polyester will be dyed yellow and polyester/cotton will become orange.

Acid dyes contain the acidic –CO2H and –SO3H groups which bond to the basic –NH groups in the amide linkages of wool, silk and nylon.

Direct dyes bond by hydrogen bonding and take well to cellulose-based fibres such as cotton, viscose and rayon which have many –OH groups.

Disperse dyes are not water-soluble. They exist in the dye-bath as a fine suspension (hence the name), and are absorbed as a solid solution by hydrophobic fabrics such as polyesters.

Teacher and Technician Sheet

In this practical students will:

• Observe and report on the findings from the experiment.
• Compare, contrast and group different materials based on results from the experiment
• Use their scientific understanding to explain the results of the experiment.

Introduction:

This is a demonstration linked to a discussion.

(Could be carried out as a class practical with dyes ready prepared as solution or post 16 students could prepare solutions from the solids).

Samples of different fabrics are placed in a single dye bath containing three dyes. The materials emerge dyed different colours.

After seeing the action of the dyes on, say, wool, students could be asked to predict the effect on silk and nylon, which are polyamides.

After seeing the effect of the dyes on polyester and cotton separately, students could be asked to predict their effect on the mixed fabric.

Point out that this experiment can help explain some odd effects in washing machine accidents where labels and trim may emerge a different colour to the rest of the garment.

Curriculum range:

Secondary students could do this for interest and entertainment, and post-16 students if the structures of the dyes and the types of bonding between dye and fabric are to be discussed in depth. It links with:

• reporting on findings from enquiries, including oral and written explanations, displays or presentations of results and conclusions;
• using straightforward scientific evidence to answer questions or to support their findings;
• comparing and grouping together everyday materials on the basis of their properties;
• knowing that some materials will mix, while others will not;
• knowing that some liquids that do not mix can be turned into emulsions; and
• build a more systematic understanding of materials by exploring and comparing the properties of a broad range of materials.

Hazard warnings:

Wear eye protection.

Disperse Yellow 7 is a SKIN/EYE and RESPIRATORY IRRITANT. The others are of LOW HAZARD but may still irritate some people’s skins and their dusts may irritate the respiratory tract. 

Plastic gloves are recommended. It is the responsibility of teachers doing this demonstration to carry out an appropriate risk assessment.

Equipment:

• 4 beakers (400 cm³) (or 3 beakers (250 cm³))
• 4 disposable plastic pipettes
• Stirring rod
• 4 large watch glasses or Petri dishes
• 1 pair of tongs or tweezers
• 1 pair of scissors
• Access to a top pan balance weighing to 0.01 (if preparing from solid)
• Spatula (if preparing from solid)
• Weighing boat (if preparing from solid)
• Bottle of distilled water
• Thermometer 
• Bunsen burner
• Tripod 
• Gauze
• Heat resistant mat
• String and paper clips, to make a ‘washing line’
• Crocodile clips or clothes pegs 

The quantities given are for one demonstration. (Class practical indicated also)

• Samples of the following fabrics in white: wool, silk, nylon, cotton, polyester, cellulose acetate (‘triacetate’), polyester/cotton mix. About 1 cm² of each fabric or a few cm of thread will be sufficient. 
• 0.05 g of each of the following dyes: 
  • acid blue 40 (low hazard)
  • disperse yellow 7 
  • (skin/eye/respiratory irritant)
  • direct red 23 (low hazard)
  • or 10 cm³ of solutions of the dyes ready prepared (per group)
• A little dilute hydrochloric acid (0.1 M)
• Sodium chloride (if carrying out the extension activity) (low hazard)
• Alum (if carrying out the extension activity) (low hazard)

Technical notes:

Nylon can be difficult to obtain and it may be necessary to try a second hand clothes shop.

Muslin squares (50 cm x 50 cm) are also available.

The dyes can be prepared as a solution for the students before use in a class practical.

Higher key stages can prepare the dyes using a fume cupboard.

Larger samples of material in larger volumes of dye can be used if the audience is large. A ‘washing line’ is useful, on which to hang samples to dry with clothes pegs, crocodile clips or paper clips.

Results:

This practical works well and can be adapted to use as both a demonstration, a class practical and for post 16 students to do for themselves.

Good results can be obtained on the following materials (both on threads and whole pieces for some of them):

• Cotton 100% 
• Polycotton 65% 35%
• Polyester
• Nylon

Using a salt (mordant) in the dye produced a deeper colour.