Hello Ivan,
Yep, you did it right!  Otherwise I wouldn't be reading your message!  Welcome
to the group!  There is no better place in the universe to learn about shells
and shelling.
Is your shell really, literally, a foot and a half in length?  If it is,
identifying it isn't too tricky - it's the "horse conch", Pleuroploca gigantea
(the second-largest gastropod or snail-type shell in the world).  You did
mention a "nice pink color".  If you are referring to the interior of the
shell, that description would lead me to suspect Strombus gigas, the pink
conch or queen conch, which is also found in your area - but that species
doesn't reach 18 inches - 12-13 inches is a large one.
In either case, you might be interested to know that the "tough brown crud" on
the outside of the shell is a material actually produced by the animal itself.
It's called periostracum.  Some collectors like their shells with the
periostracum in place, but most collectors, if they only have one specimen of
a species, prefer to remove the periostracum, because in most cases the shell
is, of course more attractive without it.  Don't try to scape or chip it off -
dissolve it.  The most common method of doing this is to immerse the shell in
a solution of chlorine bleach (Chlorox or equivalent).  For a big shell like
that I use a 5-gallon plastic pail with 1 gallon of Chlorox to 3 or 4 gallons
of water.  Lower the shell down into the solution with the spire (pointed end)
down, so the solution can flow inside the shell.  That way any meat of other
material inside will also be dissolved away.  Leave it overnight, then just
rinse it off and you'll have a well cleaned shell.  If you collected this
shell alive, you might also want to save the operculum, the hard, disk-like
object attached to the animal's body which acts like a door when the animal
withdraws.  Almost all collectors try to have the operculum with a shell when
possible.  If you throw it away, and later develop a real interest in
collecting, you'll wish you hadn't.  Don't clean the operculum with bleach
though - the bleach can damage it.  Good luck!
Regards,
Paul Monfils