That is a beautiful bike! If that is the kind of thing you find in that black hole, I'd like to come over.

The chain skips on the rear, I'm guessing? If the chain rides over the cogset, you could have a chain that is too narrow for the cogs (like a 9 or 10 speed chain on a 5 speed rear cluster). If the chain skips after engaging the cogs, then you need a new freewheel. It could be operator error, but you'd quickly get your shifting fingers bio-adjusted, and the problem would go away...if the problem is with the front, then the operator is not shifting firmly enough from one chainring to the other, or the front derailleur is misaligned.

Good luck!