Just as the title reads, I want to know if it's possible to make soap using left over lye water. I can't test right now as I don't have everything I need on hand, but I will try as soon as lockdown ends, just want to know if any of you have tried this or heard of someone doing this?

Never heard of this, but I think that would be super cool

In general the water would contain traces of Naphtha, so you could just boil it for some minutes, then all the Naphtha should have vanished.

Then you would need to somehow correct the pH to have it not OVERLY basic and then it would just be a big pot of water with various plant alkaloids remaining. Not any other harmful components ... But maybe you should need more flavor to this, so it may smell actually like something nice.

I believe the hard part is to correctly filter the basic solution to avoid an unwanted texture in the soap. I thinked about tanin extrzct in my soap but i never thinked reusing basic doup like this.
It may give an interedting color to the soap and maybe a good smell
👍

You probably could, but soap is most easily made using a calculated recipe... if I understand correctly: 3 moles NaOH per mole of triglycerides, adjusted to leave a small amount of fat (generally a few %) to avoid drying your hands out too much (superfat or lye discount). Too much or too little lye would probably make undesirable or ineffective soap (for modern tastes).

I think avoiding oil waste makes more sense than avoiding wasting lye.

Sorry for the double post, just trying to bump after my unnecessary discouragement.

On second thought, you're probably using a small mass of lye (like ≤ 50g or so), so that would probably saponify somewhere around less than a pound of triglycerides. So it really wouldn't waste that much oil even if you ended up not using the product. Maybe you could use the pH to estimate... or just take a guess. Saponification may take a day or two at room temperature (i.e. cold process), and only then will you be able to evaluate excess fat or lye... after it has already turned hard. So you might have to reprocess it to adjust if required.

As an aside: I just used some rancid olive oil for soap. Way too much bar soap now that most other people wouldn't want... no fragrance and it looks very homemade, lol. Pretty easy, quick and inexpensive though.

Glad to hear of your (relative) success, RoundAbout.

When planning to make MHRB soap, the most responsible thing to do is pre-extract any psychoactive alkaloids before the saponification. This helps to avoid surprise intoxications with home-made hand-care products. Unexpected union with the godhead might not be the most fitting thing for Aunt Maisie on a Thursday afternoon.

It's up to each and every one of us to look out for Aunt Maisie. Keep up the good work, folks!