What causes pocks or bubbles?

[Derlowemann]

I have a 1987-D and a 85-D that has pocks or what looks like bubbles on the front and back of the penny. What causes this?
Again, the detail with my scanner is not that great but you get the idea, it is much worse than it looks in the pic.
I also have another 1985-d that has all kinds of extra crud in each row of the columns of the memorial, it may be hard to see too but you can make it out and this too is worse that the pic shows.
I also have a 1983 that would not come up for a picture, but it looks like a worm trail, like something under the surface that goes up from the "FG" along the last column to the two end corners of the memorial.
Any thoughts? Thanks, Anton

[mustbebob]

Failure of the copper plating to properly adhere to the zinc core is the culprit here. Most of the problems occurred when the blanks were made due to inadequate cleaning, or some contamination on the core before plating. The early 80's were terrible for this, and you can still see some examples of it today.

[jpl6332]

the zinc core contamination as Bob has said. I wonder how many pristine examples exist without the obnoxious gas bubbles, I am betting the population is low, as an example I see 1982 Small Date Zinc Rolls selling in the $45-90 dollar range. That is also because that Pop is small too but also because of the nasty balck marks as well., even so there are other ztinks that have what appear to be additional copper plating ( maybe replated) I don't know...any thoughts on Mint replating...some of the Zincs look so thick under the scope.

[jcuve]

From what I recall Mike Diamond confirmed that the bubbles appear right after the strike, presumably as the heat generated from the striking process becomes the instigator that causes the contaminants under the plating to gas. I would also imagine that the heat also helps to facilitate the malleability of the metal resulting in the final distortion of the copper surface to easily form over the bubbles.

The evidence sited for such a conclusion was (if I recall correctly) that off-centered strikes have shown bubbles to only appear where the coin was struck by the dies, as opposed to the entire surface. I however do not have an example on hand or any specific sources to site where one can obtain pictures of such off-centered coins with plating bubbles.