Shaving soap

Method

1. Get ready

   Put on splash goggles, gloves and long sleeves, and keep them on until the soap is in its tins. Weigh 200 g stearic acid, 125 g coconut oil and 25 g shea butter into a slow cooker, 100 g olive oil and 50 g castor oil into a jug, 225 g distilled water into a heat-proof jug, and 43.7 g sodium hydroxide and 45.4 g potassium hydroxide flakes into two dry containers; close the flake tub at once, because it pulls water from the air.

2. Make the lye solution

   At an open window, stir the sodium hydroxide and then the potassium hydroxide into the water a little at a time, always lye into water, never the reverse. It fizzes and gets very hot; keep it away from aluminium, which it attacks, and let it cool below 82 °C (180 °F) while you melt the fats.

3. Melt the fats hot

   Melt the stearic acid, coconut oil and shea butter in the slow cooker on high, stir in the olive and castor oils, then turn the cooker to low. Keep the blend above 60 °C (140 °F): stearic acid sets at about 55 °C (131 °F) and starts to crystallise if the fats cool towards it.

4. Pour in the lye without stopping

   Pour the lye solution into the fats in one steady stream, stirring hard with a sturdy spatula as it goes in. The batter thickens to a paste almost at once; that is the stearic acid turning to soap on contact, not a failure, and a slow dribble only makes lumps.

5. Work it smooth

   Break up the paste with short bursts of the stick blender and the spatula until no liquid lye pools anywhere in the pot and the soap looks like even, thick mashed potato.

6. Cook it through

   Cover and cook on low for about an hour, folding the soap over every 15 to 20 minutes and scraping the edges, which cook first, back into the middle.

7. Check it is done

   It is ready when the whole mass is translucent, like petroleum jelly, with no opaque white patches when you fold it. If you have phenolphthalein, a drop on a smear should turn only a faint pink slowly; an instant, vivid magenta means another 20 to 30 minutes.

8. Make the clay slurry

   While it cooks, stir the 2 tsp of bentonite clay into the 20 g of glycerin until smooth, with no lumps left.

9. Finish off the heat

   Turn off the cooker and stir the clay slurry through the hot soap until the colour is even.

10. Scent it below 82 °C

    Let the soap cool to below about 82 °C (180 °F), then stir in the cedarwood and vetiver oils quickly, before it stiffens. Vetiver is thick, so warm its bottle in your hand first.

11. Press into tins

    Spoon the soap into tins a little at a time, pressing each spoonful down hard to push out air pockets and tapping the tin on the bench, then smooth the tops. It fills about eight 100 g tins.

12. Let the pucks dry

    Leave the tins open somewhere airy for six weeks before you put the lids on. The soap still has water to lose, and it firms up and shrinks slightly from the sides as it goes.

13. Load the brush

    To use it, soak a brush in warm water, shake it out and swirl it over the puck for 20 to 30 seconds, then build the lather in a bowl or on your face, adding a little water at a time until it is thick and glossy.