Use a cheese grater to grate a mild bar soap into a large bowl until you have 2 cups. Use the smallest shred size on the grater.
Add 1cup of washing soda and 1 cup of borax to the bowl of grated soap.
Put on rubber gloves, and mix the dry ingredients thoroughly by hand.
Add ½ tsp. of your favorite essential oil to the mixture if you want to add a scent to your detergent. Stir the ingredients thoroughly again.
Run the mixture through a food processor if you would like a finer washing powder. The finer the powder, the faster it will dissolve during washing.
Store your homemade washing powder in an airtight plastic container.
Add 1 tbsp. of your washing powder to a light load of clothes. Use 2 tbsp. for a larger or more soiled load. Do not be concerned if you don't see lots of suds. Homemade washing powder does not lather up like store-bought brands.