Probably used clear epoxy. That is a pretty sweet looking floor! But, is it legal? The cost in pennies would be $2.56 per ft^2 if you laid them out in a cubic pattern and $2.88 for the diagonal pattern that they used. That's cheaper than tile and most laminate flooring.
Any way you want to look at it it's a bad idea, many have been mentioned. Sure you could put a coating on the floor, but what kind of problems do a coating carry with it ? Kitchen floors tend to get wet, can you imagine trying to retain your footing on a slick acrylic or epoxy when it's wet ? Same thing for your store Matt. How many lawsuits do you want for people falling when they walk in with wet shoes from rain or snow ? Then of course you have the issue of how often you have to put a new finish on the floor because of how quickly the one you have gets covered in scratches, dings, and scuffs. And you can't just wax acrylic or epoxy. This is one of those things that people do because they think it would be cool. But they don't think it through and they end up wishing they had never thought of it. I spent 40 years in the construction business building homes and commercial buildings. You cannot begin to imagine some of the things I have seen people come up with !
Melting down cents currently is against a US Treasury rule. That rule has not even been challenged in court, and will most likely be withdrawn once copper cents are not common any more. Nothing says you cannot do what you like with your coins. Doug, boy you are just against this idea huh? I like it. I would think you could find some kind of binder to set these in place and fill in the gaps, then simply apply a non-skid top coating. I have seen lots of slippery material used for floors, they are simply prepped correctly, and maintained.
