Egg dyeing is a simple and common activity. Egg are dyed for Easter celebrations as well as for other decorative purposes.The Chinese will dye their eggs red during birthdays to signify good luck. When an infant reaches one month old, eggs dyed red will be distributed to all relatives. What is the chemistry behind egg dyeing? The shell of an egg is composed of about 95% crystal of calcium carbonate. Covering the surface of the shell is a thin organic layer called the cuticle. This cuticle is mainly protein in nature. It is this protein material that is necessary in dyeing process.
Most commercial food colourings are acidic or anionic in nature. They may contain carboxylate (-COO=) or sulphonate (-SO3H) groups. These are able to form salt linkages with the amino group (NH2) present in the cuticle. The dye is thus attached unto the egg shell. In most recipes for egg dyeing, vinegar is usually added. Vinegar provides hydrogen ions (H+) which are able to combine with the amino groups (to from NH3+) and create more reactive sites for salt linkages. Thus, at lower pH, the amount of dye adhering to shell increase
1 M sodium hidroxide
1 M hydrochloric acid
Red food colouring
Universal indicator paper
1. Prepare a stock solution by adding 50 cm3 of red colouring to 1000 cm3 water. test its pH using universal indicator paper. The paper will by dyed red, so rinse in distilled water before comparing the colours
2. Pour 100 cm3 of the stock solution into beaker. Adjust its pH to 2 by adding dilute hydrochloric acid dropwise
3. Prepare pH solutions of 4 and 6 following procedure 2
4. Prepare pH solution of 8, 10 and 12 by adding dilute sodium hydroxide dropwise
5.Check that colour of the dye you have chosen remains unchanged by acid or alkali addition
6. Put a chicken egg into each of the dye solution and leave for 10 minute
7. At the end of 10 minutes, remove the eggs and allow them to dry at room temperature. Compare the colour intensity of each egg
At which pH is the colour darkest
At which pH is the colour lightest
8. After drying for half an hour, rinse the egg in the distilled water. Compare the colour again. At which pH is the colour fading greatest?
9.Try different food colours and make for yourself beautiful Easter eggs
1. What is the effect of dye concentration on the egg?
Pour 50 cm3 of the stock solution in a beaker. Add distilled water to the 10 cm3 beaker mark. You are diluting the stock solution by half. Label this beaker 1. From beaker1, pour 50 cm3 ofthe solution into another beaker and dilute to the 100 cm3 mark with distilled water. Label this beaker 2. By successive dilutions, you can vary the concentration of the stock solution. Put 10 cm3 of vinegar into each beaker. immerse an egg into each beaker and observe the colour after 10 minutes
2. Vary temperature at which dyeing take place. Repeat this experiment with dye temperatures at 10°C, 30°C, 60°C, 80°C. Is there any difference
3. Can duck eggs, quail eggs, sea shells, snail shells and bones be dyed as in the experiment
4. Since the eggs shell is mainly calcium carbonate, do marble chips adsorb dye as readily as egg shells? Repeat your experiment using marble . Can you experiment result?
5. Does adding sugar or salt to the dye solution affect dyeing
6. Soak an egg for about 2 hours in 5 % EDTA solution. This is to remove the cuticle. Rinse with water and then dye the egg as before. What do you notice?