Another few hours passed, and the pill furnace was filled with useless liquid. Not a single successful pill had been refined. Chen Xun remained calm and composed, entering a meditative state to analyze.

"These spiritual herbs are truly peculiar. The difference in age makes such a huge impact."

Chen Xun thought to himself. The same Foundation Establishment auxiliary herb, with just a ten-year difference in age, required a different level of heat and technique.

This was completely different from when he refined Heavy Feather Pills and Qi-Enhancing Pills. The control over the heat had to be precise down to the year, no wonder it couldn't be refined during the Qi cultivation phase.