Cove molding is a variety of crown molding with a concave profile. I don't find that it makes the ceiling look higher; some experts say that by drawing attention to the ceiling, the ceiling may in fact look lower. To counteract that, paint the ceiling a lighter colour than the walls. Crown molding does make for a smoother transition and is characteristically used in more expensive traditional homes. Or in homes that are aspiring to a traditional look.

Crown mouldings are made of polyurethane and other foams, wood, pre-caster plaster and cast-in place plaster.

Here is a link that might be useful: Balmer Architectural Mouldings

Saw a show on public television where in an old world country,italy if i remeber correctly, they still cast plaster mouldings the same way they have been doing it from the get go.It was pretyy amazing that some old world traditions are still happening today!

I would like to see some cast in place mouldings at some point as well.Maybe somewhat of a lost art?

One of the "This Old House" episodes with Bob Vila showed a Carolina craftsman doing exactly that, matching old plaster with new.

He took the profile of the existing moulding, then built a wood tool that matched the profile--a large box like affair.
(I wish I could find a pic or even the precise terminology!)

First he put loads of plaster along the wall/ceiling angle he was working on. Then he kept running the box through the plaster, gradually shaping it to a perfectly adhered seamless moulding. Way harder to do than describe!

Here is a link that might be useful: Making Custom Plaster Mouldings

Awesome t.o.h.video! Thanks worthy!