The recipe comes originally from Arkansas Soaper. I don't make as much at one setting as she did, so my measurements are
3 Cups Borax
2 Cups Baking Soda
2 Cups Washing Soda
2 Cups Grated Soap
The washing soda is sodium carbonate and is found in the pool cleaning department of any major retailer. For the grated soap, I use handmade soap I buy from some fabulous sellers. I usually buy mine from CosmicCleanBody If you have a favorite handmade soaper, see if they will sell you their "uglies"...the soaps that aren't quite up to par but still smell lovely.
I followed her directions for the powdered soap, and she is very correct that it's way easier if you grate the soap with a salad shooter. I too found mine on Ebay and it works great.
Once the soap is grated, and your powdered items are measured out (wear a mask to keep from inhaling the borax and washing soda.) I add a bit of soap and a bit of powdered materials into a blender to blend it super fine, so it washes correctly.
Follow her directions and pulse the blender to grind up the ingredients. This keeps it all soft and powdery!