Hi Kephra, much respect to you, your knowledge is impressive and well renowned.
I however follow rudimentary chemistry, use recipes, and didn't consider the reaction continuing beyond the reducing agent.
Without measuring the weights of the coins before and after each batch, the 200ppm+ I'm chasing is amber in colour and I've yet to have a batch take 20 minutes, or even 20 hours.
Any advice would be most appreciated.