100 g (3.5 oz) bars of soap
1 cup washing soda
7.5 ltr water
*10-ltr pot is helpful
Boil 1.5 liter of water in a 10-liter pot. Grate the soap and put it in the pot, stirring to dissolve. Slowly add in the cup of washing soda and stir until it is completely dissolved. Turn off the heat before it overflows. Remove from heat and put it on the floor. Add in the remaining 6 liters of water into the pot and stir. Cover and let the soap sit for about 24 hours and it will gel. It will look like an opaque liquid with some soft lumps. Stir and bottle it. Shake and use 1/4 cup per load.
To brighten clothes: Add 1/8 cup of white distilled vinegar in the wash (with the detergent).
To soften and strip soap residue from clothes: Add 1/4 cup vinegar as a fabric softener during the final rinse.
Remember that washing soda is caustic, so wash utensils, etc. thoroughly with soap and water after contact with it.
Optional: add fragrance if desired (see recipe below):