Gardener's pumice scrub bar

Method

1. Get ready

   Open a window, put on splash goggles, nitrile gloves and long sleeves, and line or set out a 1.5 litre loaf mould. Wear a dust mask while you measure the pumice, which is fine rock dust.

2. Weigh everything

   Stir the tub of palm oil right through, since its hard and soft parts separate, then weigh 300 g coconut oil, 250 g palm oil and 100 g shea butter into the pot. Weigh 250 g olive oil, 50 g jojoba oil and 50 g castor oil into a jug, and pour 30 g of the olive oil into a small bowl for the scrub.

3. Make the lye solution

   Weigh 280.6 g distilled water into the lye jug and 138.2 g sodium hydroxide into a dry container. At an open window or under the extractor fan, pour the lye slowly into the water, never the reverse, stir until clear and leave it to cool, labelled and out of reach.

4. Wet the scrub

   Stir 4 tbsp (45.5 g) pumice powder and 17 g (about 2 tbsp) fine cornmeal into the 30 g of olive oil to a gritty paste with no dry pockets.

5. Melt the fats

   Melt the coconut oil, palm oil and shea butter on the lowest heat, then pour in the rest of the olive oil and the jojoba and castor oils. Let the oils and the lye solution each come to 38 to 43 °C (100 to 110 °F), warm enough to keep the palm oil fully melted.

6. Blend to light trace

   Pour the lye solution into the oils down the shaft of the stick blender, then pulse for a few seconds at a time, stirring between pulses, until light trace, when a drizzle leaves a faint line that sinks back within seconds.

7. Add the scent

   Stir in 20 g lemongrass and 10 g Atlas cedarwood essential oil with a spatula.

8. Thicken and add the scrub

   Pulse a little more, until the batter reaches a pudding-like trace that holds a drizzle on its surface: thinner batter lets the pumice sink to the bottom of the bars. Stir in the pumice paste by hand until the specks are even.

9. Pour and insulate

   Spoon or pour the batter into the mould, tap it firmly on the worktop and smooth the top. Cover it and wrap it in a towel; this recipe gels readily, which is fine.

10. Clean up

    With your gloves still on, wipe the batter off the pot and tools with paper towels into the bin, then wash everything in hot soapy water.

11. Unmould and cut

    After 24 to 48 hours, when the loaf is firm, put your gloves back on, unmould it and cut it into bars about 2.5 cm (1 in) thick with an old straight knife or a wire cutter, since pumice blunts a good blade.

12. Cure

    Stand the bars on edge on a rack with air around them, out of the sun, for four to six weeks, turning them every few days.