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[BKARTS] A sheep of a different color?

There is a class of chemical substances which exhibit color reversibility called redox (for reduction/oxidation) compounds; some are pH sensitive and some of those are sulfonates which find wide usage as dyes and coloring agents, brighteners, and detergents. Apropos the initial question, colorless to blue and vice versa is the most common color change closely followed by colorless to red.
I first encountered the phenomena many years ago when a book I deacidified turned dull pink after about 15 minutes. I had only spot tested the ink for a reaction to the alkaline solution and having never seen nor heard of the phenomena before I went into cardiac arrest, my suddenly attenuated career flashing before my eyes. Luckily the color was reversible by washing in a slightly acidified water bath followed by buffering in a pH 8 solution. A higher pH made the pink return.
The machine made paper was an esparto made in England before the late1950's and as far as i know had undergone no previous treatment. I've never seen a recurrence.
Best, James

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