I've never heard of this before? Is it for brushes, or is it hand soap?
I'm back with too much information, as usual. But i used to use this stuff in the late 1960s and 1970s, so i have fond memories...
Dr. Bronner's is an all-natural liquid castile soap. Besides the unscented, it also comes scented with pure natural oils of peppermint, or eucalyptus, or lavender, or almond, or any of several other scents. The original version went on the market since 1948. It has been sold in health food stores for several scores of years. It was available in bulk - you could fill your own bottles - or pre-packaged from 2 oz. to a gallon. The soap was recommended for washing everything - hands and body, hair, dishes, hand laundry...
The labels could be a bit difficult to read because Dr. Bronner - who was the third generation in his family to make soap commercially - covered them with meaningful spiritual quotes urging peace and understanding among peoples. The brand was hugely popular with hippies, health food enthusiasts, and other green sorts of people, before the phrase "green" became a nearly meaningless buzzword. And the soaps were featured in the original Whole Earth Catalogues.
There's even a webpage where you can read what it says on each of the different labels! because each of the eight labels has different messages.
http://www.drbronner.com/dr_bronners_philosophy.php
It was always a pleasurable moment while out shopping to stop in front of the soap display and read the labels.
The good Dr. died 1997 and his sons and grandsons took over the company. They didn't change the beloved product, although they did modernize the labels, removing the long quotes, to make them easier to read. This caused a furore - they got lots of complaints from loyal users. So they returned the labels to the way i remember them from the late 1960s.
Since then they've added hemp oil, become certified organic, sourced their ingredients through certified fair trade sources, gotten their products certified as not animal tested, and packaged products in bottles made of 100% post-consumer recycled plastic. And they've expanded their product line beyond liquid and bar soaps.
Good stuff.