1 bar Fells Naptha
2 cups Borax
2 cups Washing Soda
5 gallons water
Shave Fells Naptha. I use an old cheese grater to do this. Boil the shavings in 1/2 pan of water, stirring constantly over medium heat. Be sure to stir constantly until completely dissolved, otherwise the soap will overflow all over your stove top. (I've had this happen and it's not fun to clean up.) It is also important to use an old pan that you will dedicate to soap making because you wouldn't want to use it to cook soap and then cook food in it.
Fill a 5 gallon bucket with hot tap water 3/4 full. Dissolve 2 cups Borax and 2 cups washing soda in bucket. Dump the dissolved Fells Naptha into the 5 gallon mixture and fill the remaining space with water. Stir with a large spoon (again dedicated to soap making), cover and let sit until cool. Do not open until completely cooled (around 12-18 hours) this allows the soap to set and turn to gel. I mix mine, cover, and let sit overnight.
After the soap has set it is ready to use. I use an old measuring cup to dispense mine, but my sister in law fills her old laundry soap containers and dispenses hers using those.
This laundry soap costs $2.57 to make 5 gallons, a typical load of laundry uses 1/2 cup laundry soap to clean your clothes. (I use a full cup just to be sure, plus it's cheap enough that I can use as much as I want really.) In order to use a 1/2 cup laundry soap per load using homemade laundry soap you will spend $0.03 per load, if you choose to up it to 1 cup it will only cost $0.06/load. A bottle of Tide laundry soap will cost you almost $12 (depending on where you shop it could cost more) which means each load of laundry you wash will cost anywhere from $0.43-$0.97 therefore switching to homemade laundry soap can save you some serious dough!
The original homemade laundry soap has very little smell, therefore if you would like to add a scent you can add an additional dissolved bar of soap, you can replace the Fells Naptha with another a different bar soap, or you can buy scented soap oil from Hobby Lobby or your local craft store and add your favorite scent to your laundry detergent. Just be sure that whatever you add will not effect your clothing colors. I always choose very light colored bars, and clear oils. My favorite is the lavender oil from Hobby Lobby.