Confused About Cleaned Coins

Depends on how much the eye appeal has been damaged. Originality rules the Coin World these days. For a quick dip on a MS or higher AU coin that left luster relatively intact, I would say maybe 60-85+% of normal book value depending on the collector. Anything else, except certain early 19th c. coinage (Bust halves/quarters & earlier) I value at 10-20% of book, or melt for silver/gold, whichever is higher. The only coins that still maintain a fair bit of value even when harshly cleaned or otherwise abused are certain very key dates (1877/1909S IHC, 1856 FEC, 1909-S VDB/1914-D LWC's, 1916 SLQ, 1893-S Morgan $1, CC/C/D minted 19th c. gold, so on and so forth) and other coins that will always carry a premium in ANY grade (Chain/Wreath large cents, Small Eagle early bust coins, patterns, proofs, exceptionally rare die varieties, overdates, etc.)

Ultimately it's going to be up to whomever is looking at the coin to decide how much the cleaning has affected the value. Some collectors are slightly more tolerant than others who will not accept any non-original coin of any sort at all.

There is no "hard and fast" rule, unfortunately. A good guide is to search completed ebay auctions for cleaned examples of given coins in a series and see what they tend to sell for.

Is it true that cleaning coins was a "thing" in the '50s?

For that matter, how damaging is it to use a microfiber cloth and some pressure to get that tarry gunk off an otherwise fairly, clean coin? I've been afraid to do it with a couple of fair finds from pocket change, in case it damages the coin. I've tried it on a couple spenders just to see if it works. It gets the stuff off, but the coins are lighter where it used to be. I didn't see any scratches, but I'm not looking with a stereoscope.

I have one with a fingerprint! Just there on Liberty's cheek.

Dipping was certainly "a thing" in the 1960s when I started collecting. Silver coins, regardless of their age, were supposed to "white" for many collectors. Most every Bust Dollar you saw offered for sale was white even in the circulated grades.

There were collectors who collected toned coins, but some people thought that they were a bit "odd." Many collectors had the attitude that toning hid wear and was therefore a way to push AUs or "sliders" on to unsuspecting collectors as Uncirculated.

My first really old silver coin was a 1799 Bust Dollar, which I bought circa 1969. It graded Choice VF by sharpness, but it had been dipped white.

It was not whizzed or polished however. What's the difference? Whizzed, cleaned or polished coins have had the metal on their surfaces moved around. That is now and long has been a big no-no.

Dipping removes a very small amount of oxidized metal with a weak acid. Purists will tell you that is just as bad as cleaning, but they are wrong in my opinion.

Dipping, if it is done properly and not too often can restore some beauty to a coin. Some naturally toned pieces can be very ugly and almost unsalable. Dipping can bring them back to life. BUT you have to be able to judge which coins will benefit and which ones will not. That is where experience and knowledge come in.

@billjones the term was I remember from Coin World was "Blast White Stunner!". Dealers listed them by the hundreds.

Because there were so many of them in the 80's and 90's I wonder whether there was a wink wink nudge nudge by the TPG's in return for bulk submissions. Or whether, like Tour de France riders of the time, dealers got so good at dipping them that they passed detection.