I found out that last month they returned some "Unc" old time cardboard milk bottle caps because: "They did not wish to take the chance of damaging them while putting them into the insert ring of the slab." Sounds like a product that is better suited for the NGC "Edge View" insert.
Actually you are both correct as it depends on the spot. In one "study" to get rid of them it was found that moisture from an air gun used during the slabbing process causes some of these spots to develop over time - even in an "air-tight" holder. Now, there are multiple filters in place. Also, pressure on the Mint caused them to release their findings on Mint-caused spots.
@BooksB4Coins ...I DIDN'T and I could not believe you left such a nice post after his challenge. I decided to edit a well-worded response but decided not to "bash" the little girl.
I remember those old milk bottle caps back in the days when a milkman delivered the milk products to your home. Then they changed them to the aluminum caps with the crimped edge. It sounds to me that they might have slabbed them if they didn't think there would be any damage. Chris
SuperDave: Those milk spots on the Morgan look about the same color as most of the field: but they are surrounded by a much darker field darker which might reduce its value.
"Milk spots" appear to have no correlation whatsoever with the contours of the struck coin. They look like random splatter on a FLAT surface, and that splatter pattern is not affected by the design relief. This indicates that the surface contamination originates PRIOR to the strike.
Whatever causes the spots originates prior to striking. So the spots exist from the beginning, but they can become more visible after time. Under certain lighting conditions, they can be revealed before they become visible under normal conditions.
I agree with most of your replies; however, the identical color contamination appears on SE as large "stained" patches as well as spots. Many of the larger patches resemble a "wiped area" which could also be prior to the strike. Nevertheless, I'll bet there are cases of BOTH planchet contamination and post mint factors causing the stains/spots.
I agree w/most of your post; however, some of the stains occur as v. large patches as if the coin were wiped. IMO, the spots or stains can result from BOTH pre strike contamination to the planchet or post strike contamination to the coin. I wondered where the one above went so wrote this.
Perhaps I can make this somewhat easier for you... http://www.dictionary.com/browse/appear http://www.dictionary.com/browse/visible Make sense now? Now, are these "certain lighting conditions" absolute in the ability to reveal said spots prior to becoming "visible under normal conditions"? Instead of alluding to this wonderful method, perhaps you should share it to the benefit of the collectors in general, or at least just on this forum. Considering the scope of the problem, and the established and widespread belief that they can indeed show after a period of time, including while in a slab, this surely infallible method of identifying could be of immense benefit to those who choose to collect such material, and even I, as someone who doesn't, would much love to learn of it.
@BooksB4Coins This may be from Daniel Carr and he knows his stuff! Hope he replies. I know people use fluorescent and BLACK LIGHT in numismatic authentication and grading. We'll see....
have You know, you could have just politely asked "what lighting conditions ?" instead of all that. Ultraviolet. As in a mineral light (combined long & sort wave UV). This will illuminate certain trace compounds (like mint detergent residue) on the coin. These compounds can, over time, cause microscopic etching of the silver surface (which is what permanent "milk spots" are). If you properly "dip" a coin to remove these compounds, that will mitigate further etching (but dipping won't do anything about etching which has already taken place). PS: Plastic absorbs UV light, so the coin must be outside of the holder for such inspection.
I am also astonished that nobody has been able to figure out where this actually comes from (or I have just missed that post). I have an Accented Hair Kennedy Proof set that is excellent except for those spots. Also, 99% of the spots are on the obverse. Reverse is clean but for one or two tiny spots, and all other coins in the proof set are clean, silver and non-silver. So we just have to live with them and there is nothing that can be done?
