I am a Lush bubble bath addict, and decided I needed to make it myself or I would go broke. I did a lot of testing with different recipes, and this one is a combination of many, and works great. I'll post pictures soon.
1/3 cup of cream of tartar (you can also substitute corn starch)
1 cup of baking soda
1 cup of sodium laurel sulfoacetate (SLSa)
1/3 cup of glycerin liquid (plus more if needed)
soap coloring - as much as desired
Fragrance Oil - as much as desired (i used about 1/3-1/2 oz)
The Sodium Laurel Sulfoacetate (SLSa) is the only ingredient I couldn't find locally. I bought mine at http://www.bubblesnlights.com
. It seemed reasonably priced and they had lots of yummy fragrances too. When you are working with it, you need to wear a mask. It is not supposed to be harmful to breath in, but you will cough ALOT.
As for the coloring, I use powdered. It was easier to get the color even throughout and it colored the bath water nicely too. If you use liquid, it will affect how much glycerin you use.
Add a lot of frangrance. Remember this is going to make enough for about a dozen or so bathtubs full of water. It'll seem a little overwhelming when you are mixing it, but it will be okay when you slice it up and store.
Mix all the dry ingredients together (including coloring if you are using dry). I used my hands in rubber gloves. The SLS is a very fine powder, so just swish everything around until it is mixed. Add the frangrance into the glycerine and drizzle both over the dry ingredients while mixing with your other hand. If you are not happy with color saturation, add more. When it is all mixed, take a clump in your hand and see if it will hold its shape. If it is crumbly, add more glycerine. When it is the consistency of dry play-doh and it holds it shape, you are done. Now, you can take the whole thing and put it in a soap mold, and let it sit for 30-60 minutes. When you unmold it, if it does not stay together, just put it back in your mixing bowl and add more glycerine. If it is ok, you can slice it and let dry for a day or two. I usually cut it up into 6 slices, the cut those in half. You can also just make it into single-use sized balls or cubes or put it into smaller soap molds.
After it has dried for a day or so, you can wrap it up to store. It should is supposed to last for 2 months, but it never lasts that long at my house.
To use in your bath, take one of your slices and crumble it into the running water.
I'll try to post pictures tonight of the finished bubble bath.