I've been using Borax the following way since the late 90's and love it!
1/2 cup Borax in 1 gallon hot water and shake well.
Separate part of this into a bottle applicator and add whatever small amount of Castile liquid desired for shampooing. Wash twice, rinse twice with water, then thoroughly with 1 tsp citric acid in 1 quart of water. After that do a final rinse with just water. NO TANGLES EVER...only soft manageable hair!
There are lots of posts on using Borax as Shampoo. I had to try it but I had some problems no one seemed to mention. My final review is I LOVE IT and will never go back to regular shampoo.
I have very oily hair and shampoo daily or I look like I dumped grease on my head. I mixed up a few spoons of Mule Borax in a 4 cup bowl and poured it on my head then rinsed. I looked like I had dreadlocks!!! My hair all clumped together and looked horrible. The Borax couldn't clean my hair. I had too much buildup. So I used a bit of dish soap for my next shampoo to strip my hair and also a higher concentration of Borax.
I kept trying it and figured out that with our water (TX gets its water from lakes so its got lots of stuff in it) and my oily condition I had to do the following : at least 1/4 -1/2 cup or more of Borax in 8 cups of hot water. Stir and wait for crystals to settle to the bottom. Wet hair with water and pour, scrub, pour scrub, etc at least 4 times with no rinsing between. Then rinse hair in fairly hot water. That's it. My best guess is that it takes a very strong concentration to loosen the dirt / oil and repeating the scrubbing / washing helps loosen it all from the hair shaft. Then the hot water helps to remove it all.
The whole process is actually faster than when I would shampoo. I will admit about once a week or two I do use regular shampoo to strip any excess oil that seems to build up. I also do a heavy conditioning treatment at that time. Otherwise I don't need any conditioner on a daily bases which is amazing because my hair is long and tangles easily.
To anyone trying Borax I suggest really stripping your hair first of all the buildup. Use dish soap to wash first, then do the Borax wash. Then just use Borax every time you wash thereafter. Then you won't have the dreadlock look the first time. You need to make the Borax water as strong as needed for your hair and your water.
Benefits: less oily hair, no reaction or sensitivity, hair fallout has decreased dramatically, hair dye sticks to hair much better and stays much longer with less fading!!
Additional benefit: it runs over face and my redness has decreased along with decrease in pore size and overall face coloring has evened out. Wonderful side benefit. I wrote another post about how well this works for your face!!