The process of recycling soap bars and making them into new soap is called rebatching. This process involves shredding up the old bars, reforming and reshaping them into new bars. The optimal soap to use for this process is plain white soap that is neither perfumed or dyed. However, if you have leftover soap from a soap-making project that went awry, you can use that as well.
Shred the bars of soap with an old cheese grater. Place the shreds in a microwave-safe glass bowl. Add the water and food colouring. Stir gently with a wooden spoon.
Cover the bowl with cling film and place in the microwave. Melt the mixture in the microwave. Use a medium setting and melt for three minutes.
Use oven gloves and remove the bowl from the microwave. Check the soap and see if it has melted. Stir with the wooden spoon, if necessary. Melt in the microwave in three-minute increments until the mixture is translucent and easily stirred. The water should be well incorporated into the mixture.
Remove the glass bowl from the microwave. Sprinkle the dried herbs on top of the mixture and stir in using the wooden spoon. Make sure the herbs are thoroughly incorporated.
Add the fragrance or essential oil and stir in gently with the wooden spoon.
Scrape the soap mixture into heat-resistant moulds. Pack the soap down well and smooth the tops with the wooden spoon. Cover the moulds with cling film and let the soap set until cool. You can speed up this process by placing the moulds in the refrigerator.
Remove the soap from the mould. If you haven't used a bar mould, cut the soap loaf into bars and allow to air-dry for a week. After a week, package the soap in decorative papers and add a ribbon tie if desired.
Always use hot mitts or potholders when handling the glass bowl. Be careful when handling the hot soap mixture; it can easily burn your skin.