You dissolve a small amount of castor oil in denatured alcohol, then leave the patches out to evaporate out the alcohol. You're not supposed to have any residual alcohol in the patch fibers. A fine amount of castor oil is absorbed into the patch fibers, yielding essentially a dry patch. There is no excess oil in the patch to react with combustion and residual fouling is at a minimum. I've found it to be very clean in PRB applications, and also for cap &* ball revolver paper wads, musket TOW wads and also vegetable fiber wads for muzzleloading shotgun loads. I find it works for me better than any of my previous patch or wad lubes & there is no reason for me to ever quit using my castor oil blend.
Castor oil has many industrial uses, and has been used as a 2 stroke and other engine hi temp applications due to its' temperature stability and outstanding lubricationg properties.
Here's more than what you want to know about castor oil.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015816/