Before you begin, pick some appropriate moulds to make your bombs in. I usually use rubber ice cube trays as this makes them easy to pop up, but this time I used a plastic tray designed for holding shot glasses. I coated the tray with cling film, to ensure I'd be able to get the bombs out easily.
Crush together the lavender and baking soda in a mortar with a pestle.
Pour the witch hazel, lime juice, lavender essential oil and the food colourings in to a spray bottle and shake well. This should create a nice deep purple coloured liquid.
Spray the witch hazel mixture on to the baking powder and mix continuously.
When the mixture begins to stick together, take a spoonful at a time and compact the powder it in the the moulds. Leave to dry out, this may take a day or two. When the bombs are dry, pop them out of the moulds and they're ready to use!