I have made a jewelweed CP soap for 5 years now. I started at the request of my friend who fights poison ivy every year because of her three dogs, three cats and 100+ acres of forested land with many trails. They bring it in on their fur constantly. Anyway, she asked me to make her some since she was buying online and it was expensive. The first year she provided the jewelweed from her property. Since then I know what I'm looking for and find it in ditches all around my area. I sell a lot of jewelweed soap and have repeat customers and many who tell me it's wonderful stuff and works on poison ivy, poison oak, and poison sumac as well as stinging nettles. I've never had poison ivy so I have no firsthand testimony here.
I harvest jewelweed plants in August when the plant is in bloom and very juicy. I cut the stems into short sections (about 1" - 2" long) and heat them in the water I'm going to use to make soap and the coconut oil I'm going to use in my soap. I don't worry too much about the amounts at this point, but I'll estimate about 5 pounds of jewelweed to 2 gallons of distilled water and 5 pounds of jewelweed to 1 gal of coconut oil. I heat low and slow in stainless steel pots with lids on an electric cook top to about 120F for hours (6 - 8 hours typically). I have to cycle the pot heat on and off repeatedly over those hours so that they don't overheat. The temp is sort of an average. I heat, then let it cool, then heat again, etc.
After the long steeping, I macerate the jewelweed in the pots with a long piece of wood pounded into the pot while it sits on the floor in front of my chair. Sort of like I'm muddling a mint julep but much bigger. I'm working it to release more of the jewelweed sap into the oil and water. I then separately decant the oil and water through a colander first, then again through cheesecloth, and finally through #6 coffee cone filters. This essentially removes all fibers and pulp from the water and oil. I decant the oil and water separately into 1 gal jugs with lids and then I refrigerate them both until I make jewelweed soap.
I make my CP soap with my infused jewelweed distilled water and base oils, one of which is the jewelweed infused coconut oil (18% by weight of the oils in the bar). I heat oils to about 100F to 110F. I mix my lye with jewelweed infused distilled water and wait for the temp to come down to about 110F. It might work well to mix lye with a fraction of just distilled water also and let that cool before bringing the total water to the required amount with infused water. I then proceed to make my soap. I don't add color or scent.
Before agreeing to make jewelweed soap I wanted to be sure it was justified by more than just folklore or anecdote. I'm an engineer by training and like evidences. I did find a few peer-reviewed articles about jewelweed and poison ivy that say there is a component of jewelweed that neutralized urishiol, which is the active itching agent, although regular soap is effective too to remove the itching agent. The evidence isn't conclusive as best I can tell, but it isn't considered quackery.
https://www.sciencedirect.com/science/article/abs/pii/S0378874112004382
https://pubmed.ncbi.nlm.nih.gov/22766473/
https://pennstate.pure.elsevier.com...ivyoak-allergic-contact-dermatitis-with-an-ex
http://www.bio.brandeis.edu/fieldbio/medicinal_plants/pages/Jewelweed.htm
https://www.researchgate.net/public...g_post_poison_ivy_exposure_contact_dermatitis