I'm not able to get here often, so my reply is probably late.
Producing crisp shells is really an art and science, I've learned. I
am in no way an expert, but I've done a lot of experimenting and a lot
of reading on the science of chocolate (I'm trained in science, so
things like crystalization curves are actually interesting to me.)
What is amazing is that you really have to take into account a lot of
variables that will be unique, depending on where you live and your
environment: temperature and humidy being two critical factors, as well
as where you will be "cooling" the chocolate, and whether you will be
cooling molds or coated chocolates. I'm very fortunate to live in a
very arrid environment with mild winters, so often, I can keep a room
in my house at 50 degrees, or use my patio as a "refrigerator" if my
refrigerator is full.

What works for me is a combination of factors, and frankly, if even one
of them is off a little, I get a less-than-perfect product. First is
the chocolate itself. High cocoa butter content is important. Then,
the molds. Even though they are 10 times the cost than the flexible
plastic molds you can get anywhere, I use polycarbonate molds. They
are much easier to work with, and the shine they produce is wonderful.
Keeping them absolutely clean and dry is the key to them, I've found.
And when working with them, they should be at room temperature. Next
variable is the "temper." I spent several years experimenting with
different ways to temper by hand. While I got pretty good at it, I
found that eventually I was making so many pieces I ended up springing
for a tempering machine. (I now own three). The brand I have
(Chocovision) frankly does a better job than I ever did.

For a long time, what I didn't realize was that the cooling is
critical. After you fill your molds, then drain the chocolate, then
scrape them clean (about the time the chocolate is just at the point
where it is like clay), there is an amazing science to cooling that
involves not only temperature, but humidity and air-flow. I'm just an
amateur, so I can't control those factors. I basically can either use
a cool room or a refrigerator, and most of the time, that works. If I
use the refrigerator, I try to just use it for a few minutes at a time;
I want the chocolate to crystalize and set, but not to get so cold it
risks condensation.

What I've found can cause problems is one of two conditions: the
chocolate was at too cool a working temperature when it was poured (not
so much a problem with a machine-controlled temperature) or the
chocolate was allowed to cool too slowly. In both those cases, the
chocolate blooms on the inside, and the outside is not nearly as shiny,
or it may actually show bloom too.

So, that's been my experience for getting crisp shells from molds, as a
self-taught chocolatier. Good chocolate, good temper, keeping the
chocolate at a proper working temperature (87-89 F), clean
polycarbonate molds, proper cooling - produces a shiny, crisp shell 95%
of the time.

Oh. And another factor is the filling. There is a whole science to
this, too, because the fat content and water content of the filling
determine a number of factors, such as shelf-life (how long until there
is risk of bacteria and, more commonly, mold), and fat "migration" that
will eventually alter the texture of the chocolate. This is one reason
I'm glad I'm an amateur! There is a LOT to know. But the basic thing
I've learned is that some fillings last longer than others, and some
end up causing imperfections sooner than others. Fortunately, my
chocolates are pretty good (blushing) so people eat them rather
quickly. But I don't trust mine to be good for more than two weeks if
I've used a ganache-type filling.

-Bruce