I have a quarter that looks as if the back side is a slug. The front side appears to be normal, but there's nothing on the back and no ridges around the edge.
MY guess is that it is the copper/nickel alloy that wasn't struck at the mint. Have you weighed the coin? Looks like a missing clad error combined with failed strike
Yeah the do, but if you open them with the "New Window" Icon in the upper right corner of the photo the will enlarge quite well.
The reverse looks like like someone was playing with a metal lathe and removed the reverse. It is not a mint error.
At least you started your response with "My guess.." Usually incorrect info will be corrected. Sometimes nicely and sometimes it is rather rude. If I have an idea, but completely sure about something, I'll mark the "watch post" tab and see what others think. If I'm right, I give myself a pat on the back. If I'm wrong, nobody is the wiser and I still learned something.
It doesn't just that a full size is much easier to see. I just played with your technique. It does work well. I was feeling quite ornery last night.