It wasn’t long after potassium carbonate was finally isolated as the key ingredient in potash (Antonio Campanella, 1745) that enterprising chemists got interested in refining it, taking the extra step of heating potash to burn away its ashy residues. This had the effect of turning the powder a sparkling white, which thence became know as “pearl” ash (now THAT’s good marketing).
The main use for this material was again for glass-making. Yet being such a strong alkaline it was also great for making soap (alkaline + fat = saponification which…oh heck, more on that another time). Yet the act of refining potash had the added benefit of removing the burnt wood flavor from the product, which cleared the way for its large-scale use as a leavener.
The first published recipe to call for pearlash — a type of gingerbread — was published in 1796 by one Amelia Simmons. It was the beginning of a chemical leavening revolution that would spread around the world.