Are you talking about paint brushes for use with house painting type of paints or oil or acrylic or water-color types of paints?
There are at least 2 or 3 threads here at SMF about soap for cleaning artist brushes. I'll look for them & add links if I find them.
ETA: here are some threads on the topic of soap for cleaning artist brushes:
From 2014:
Paint Brush Cleaning Soap?
From 2013:
Artist's Soap?
From 2012:
Soap for cleaning paint brushes?
From 2016:
Brush Cleaning Soaps
From 2017 not about soap for brushes per se, but does address it toward the end of the thread:
https://www.soapmakingforum.com/threads/please-help-me-recreate-this-commercial-soap.68555/
Also of interest, besides the Masters brand, which does not list ingredients, I found a couple of other brands of artist brush soaps on the market that DO include an ingredient list and both are similar:
Da Vinci Brush soap ingredients are listed:
View attachment 50525
Becca Professional Brush soap ingredients are listed:
View attachment 50526
So if you want to create an artist brush soap similar to these, you would first look for the INCI name and revert the ingredients back to their components (
see this list):
Sodium Palmate = Palm oil + lye
Sodium Palm Kernelate = Palm Kernel Oil + lye
Agua = water
Sucrose Cocoate = (
see this link)
glycerin (a bi-product of making soap)
Sodium Chloride = salt (like table salt)
Tetrasodium EDTA = a chelator (
see this link)
and last, but not least:
NaOH (not listed by itself, but indicated in the INCI name of the oils with Sodium+ the name of the oil + the suffix, "-ate" which means the oils were saponified using Sodium Hydroxide)
This same ingredient list is used in make-up brush cleaner soap at pretty steep prices as well. But they're all pretty pricey considering the amount per tiny little container.