Gather your supplies
• Block of glycerin (250-500g)
• Pyrex jug
• Plastic or metal spoon
• Liquid food colouring
• Plastic moulds (or ice-cube trays)
• Plastic loaf pan
• Sharp knife
• Essential oil (optional)
To make multicoloured soap:
Melt glycerin and add the colour. Pour into a plastic loaf pan to a depth of about 10mm. Allow to set for about four hours. Turn out and slice horizontally into 10mm-wide strips. Repeat process, using a variety of colours, until you have the desired quantity of soap strips. Layer the soap strips in a plastic loaf pan.
It's difficult to determine exactly how much clear glycerin you'll need to cover the coloured strips. Err on the side of caution by melting more than you think you'll need. If you underestimate the amount and have to pour a second layer of clear glycerin, the two layers won't adhere. If you melt too much glycerin, simply leave the excess to set and use it later. After melting the clear glycerin on a low heat, carefully pour it over the coloured strips until they're just covered. Set aside for about 24 hours. Turn out and slice cleanly with a sharp knife.
Half-fill a saucepan with water, bring to the boil, then let it simmer. Cut the glycerin into chunks, place in the jug and sit the jug in the pan. Stir the glycerin while it melts, then remove from heat.
Use an eye-dropper to add the food colouring, drop by drop. Three or four drops per 250g glycerin should do. Add in 2-3ml (or 1 teaspoon per 250g glycerin) of essential oil. Work quickly before the glycerin has a chance to set. If it sets too soon, remelt it. Pour into moulds and leave for about 24 hours.
Tip: Add ingredients such as oatmeal and and a teaspoon of honey to make a gorgeous oatmeal soap. For a finer oatmeal consistency, blend in a food processor before adding to the glycerin mixture in step 2.