I NEED to amend my instructions to say that the particular method I gave is for VERY STRONG deodorant. I graduated to this strength. I'm SO sorry for not saying that in the first place. I was just thinking to write down how I make it. I didn't start out with that strength. It's something you'll need to play with to figure out what is the correct strength for you. You're son's needed strength may be different than yours. Now, I just keep adding the magnesium chloride until it begins to show signs of taking a longer time to dissolve. When I first made this (best I can remember - I've been using this for years) I added about 1/4 of the container with the flakes, added the witch hazel, let it sit for a while, then shook it to see it was totally dissolved. If it doesn't totally dissolve, just strain it, though I've never had to do this. BUT, if you have to strain it, you've got some pretty powerful product.