1885 Morgan Dollar- ANACS MS-64

Quote:
This one is not a candidate for a dip. Dipping is math - you get a certain number of seconds the coin can be soaking in dip during the course of its' life. This is cumulative even if fifty years passes between dips. When those seconds run out, and you've won the Dip Lottery, your coin is ruined forever in a fashion the whole world can see.

It happens without warning, the time difference between "OK" and "oops" is about 1/16th of a microsecond, and no two coins have the same total tolerance. It is, quite literally, numismatic Russian Roulette. You can dilute thiourea (the acid we're talking about here) with water and ameliorate the effect just as MorganGrader said. It works well for lesser problems. The cutoff moment still exists.

This coin is dark enough to require full strength for at least 6-8 seconds to remove the color, maybe more. A strong coin will last 10 seconds or a bit longer before forever losing its' luster. I saw one the guy said he'd given 15 seconds without losing the surfaces. Once.