How does one enrobe a candy center in chocolate in such a way that you get a smooth sphere with no ugly mark where it was sitting on a rack, or hole where it was held by a skewer?
What you need, my good man, is a candy fork.
Basically it's a two-tined fork with incredibly thin tines. Dip, lift, allow excess to drip off, place on parchment (you will get a tiny 'foot' but this is normal).
unless you're talking about absolutely perfect spheres? to my knowledge this is not doable by hand, you will need industrial machinery. and the two hemispheres method will leave you with a seam.
i have heard one solution for the tiny hole left by a thin skewer is another tiny dab of chocolate and a quick blast with a hair dryer to smooth out any imperfections, but i have never tried it myself.
Adding another answer because Michael accepted that one, and I don't want it to look like he accepted what I'm going to write now.
Another way to make perfectly spherical candies is to go the molecular route. You can melt chocolate and thicken it with xanthan gum to mimic a set chocolate. Then add alginate, drop dollops of the chocolate into a calcium chloride bath. Before they set, push your candy centre into the ball of chocolate. I haven't tried this, but the theory is sound.
In order to obtain a perfectly smooth spherical coating, you will have to use a mold.
If you are hand-dipping your centers, you will get a "foot." The warmer the chocolate, the bigger the foot.
Rather than dipping your center, I would recommend you "roll" the center to coat it. Granted, this is messy, but you will probably get the closest to having a "non-footed" product.
To do this, after you temper the chocolate, put a ladle of it onto a marble slab (a dinner plate also will work). With one hand, "play" with the chocolate. It will get thicker as it cools more. When it is pretty thick, but still liquid, use your clean hand to drop a few centers into the chocolate. Roll them over to coat well with your "messy" hand. Pick up the center and place on a sheet of parchment or wax paper... whatever you are using. You can also use your finger to make a swirl on top, but your chocolates will not be perfectly smooth if you do that.
When the chocolate on the plate starts to get too thick, you just add more warm chocolate to it. Unfortunately, this is an experiential method. It takes a while to get the "feel" for this to make the chocolates as pretty and "foot-less" as possible.