First, the ingredients:
1 bar Fels Naptha laundry soap
1 cup washing soda (Arm & Hammer)
1/2 cup borax (20 Mule Team)
In our area Publix consistently carries all of these. Larger Wal-Marts generally carry the washing soda and borax and sometimes the Fels Naptha. Old-fashioned hardware stores are also likely to have all three. In a pinch you could use simple soap like Ivory, but I'd sub 2 bars because a single bar of Fels Naptha is 5.5 oz (155 gm).
Next, the equipment:
Five gallon bucket with a lid (we re-used an old pool chemical bucket, thoroughly washed, of course)
4 quart or larger saucepan
2 quart saucepan
Grater or vegetable peeler
Regular mixing spoon
Really long, sturdy spoon
The procedure is pretty simple but requires some patience. First, put 2 quarts of hot tap water in the 4 quart saucepan and set it on the stove to heat. You want it to work its way to very, very hot while you do the next step.
Next, put one quart of hot tap water in the 2 quart saucepan. Set it on the stove over low heat. While it heats, grate the soap into the water, stirring occasionally so it melts into the water and dissolves. You can use a kitchen grater or a vegetable peeler. In a pinch you could probably chew it up in a food processor but we really enjoyed the grating-the-soap part. Maybe it's a Zen thing.
Make sure the soap is completely dissolved in the hot water before you move on to the next step, and also DON'T let the soap-water mixture boil. It will foam up and take over your kitchen. Turn the burner off for a minute if you have to, to let it cool down.
Next, take the 2 quarts of near-boiling water off the stove and pour it into the five-gallon bucket. Follow this with another 10 quarts (that's 2-1/2 gallons) of hot tap water. You need the mixture in the bucket to be nice and hot so all the ingredients will dissolve. Pour the soap-and-water mixture in and stir it well. Add the washing soda and stir until it's completely dissolved. Add the borax and stir until it's completely dissolved. The hotter your water, the faster the powders will dissolve.
Isn't it pretty?
That's it! If you're desperate, you can toss some in the wash right away but I waited for mine to cool before using it. The dosage? 1/2 to 1 cup per load, depending on the level of soil-and-stink. Fels Naptha is incredible stuff - we always had great results with it when doing washpot laundry for living history demonstrations - so I expect 1/2 cup will be sufficient for most of my laundry needs.
Since all the ingredients are already dissolved, you can use it in cold water, though my experience tells me that warm water improves soap's chemical reaction with dirt and, especially, grease. I expected lots of suds because of the soap content but it really doesn't foam any more than commercial laundry detergents do. Also, since it's soap-based rather than detergent-based, it won't fade fabrics too badly.
The cost of this whole endeavor:
Fels Naptha 99 cents
Washing soda $3.99 (whole box) - 50 cents for this batch of laundry soap
Borax $2.29 (whole box) - 20 cents for this batch of laundry soap
So there you have it, anywhere from 48 to 96 loads worth of effective, relatively natural laundry soap for less than 2 dollars. If you decide to give it a try, let me know how it works out for you. So far we're pretty darn pleased.