Coving - theory:
At their simplest, moldings are a means of applying light- and dark-shaded stripes to a structural objects without having to change the material or apply pigments. The contrast of dark and light areas gives definition to the object.
Imagine the vertical surface of a wall lit by sunlight at an angle of about 45 degrees above the wall. Adding a small overhanging horizontal molding to the surface of the wall will introduce a dark horizontal shadow below the molding, which in consequence is called a fillet molding. Adding a vertical fillet to a horizontal surface will create a light vertical shadow. Graded shadows are possible by using moldings in different shapes: the concave cavetto molding produces a horizontal shadow that is darker at the top and lighter at the bottom; an ovolo (convex) molding makes a shadow that is lighter at the top and darker at the bottom. Other varieties of concave molding are the scotia and congé and other convex moldings the echinus, the torus and the astragal.
Placing an ovolo directly above a cavetto forms a smooth s-shaped curve with vertical ends that is called an ogee or cyma reversa molding. Its shadow appears as a band light at the top and bottom but dark in the interior. Similarly, a cavetto above an ovolo forms an s with horizontal ends, called a cyma or cyma recta. Its shadow shows two dark bands with a light interior.
Źródło: https://en.wikipedia.org/wiki/Molding_(decorative)#Theory
plaster - the demand for specialists
A fairly simple task would be to list dozens of professions, because the modern world is so developed that in recent years, a lot of ways to make money, and those created many years ago are still not time-barred. A good example of the latter case is the stucco, plaster ornaments and so on the external walls and internal. A person specializing in this field should have a broad knowledge in the field of construction machinery, as well as sculptural art, because the stucco was based on these two areas. To create a solid stucco are necessary exceptional manual dexterity and patience, so surely this is not a job for every man.
Some ceiling facts
Ceilings are classified according to their appearance or construction. A cathedral ceiling is any tall ceiling area similar to those in a church. A dropped ceiling is one in which the finished surface is constructed anywhere from a few inches or centimetres to several feet or a few metres below the structure above it. This may be done for aesthetic purposes, such as achieving a desirable ceiling height; or practical purposes such as acoustic damping or providing a space for HVAC or piping. An inverse of this would be a raised floor. A concave or barrel-shaped ceiling is curved or rounded upward, usually for visual or acoustical value, while a coffered ceiling is divided into a grid of recessed square or octagonal panels, also called a "lacunar ceiling". A cove ceiling uses a curved plaster transition between wall and ceiling; it is named for cove molding, a molding with a concave curve.1 A stretched ceiling (or stretch ceiling) uses a number of individual panels using material such as PVC fixed to a permieter rail
Źródło: https://en.wikipedia.org/wiki/Ceiling