Collage  ●  Assemblage  ●  Found-object Sculpture

The line often blurs among these three.  As usual, art defies definitions and categories.  Despite the blurred boundaries, some definitions can be attempted.

A found object, in an artistic sense, indicates the use of an object which has not been designed for an artistic purpose, but which exists for another purpose already. The objects are discovered by the artist to be capable of being employed in an artistic way, and are designated as "found" to distinguish them from purposely created items used in the art forms.

In 1915, the French artist Marcel Duchamp is coined the term "ready-made" to refer to everyday objects selected and designated as art.  His technique was adapted by such contemporary artists as Robert Rauschenberg, Andy Warhol and Jasper Johns.  Today the terms "ready-made" and "found-object" are used interchangeably. 

The term assemblage, as coined by the artist Jean Dubuffet in the 1950's, may refer to both flat and three-dimensional works. 

Similarly, collage is regarded as an assemblage of different forms, thus creating a new independent aesthetic whole.  This technique made its first appearance in the early 20th century as a groundbreaking novelty, but with the passing of time it has become ubiquitous. 

Oil Painting

Of course, oil painting has been around for centuries.  First, a surface must be prepared.  The surface can be just about anything, but a traditional artist's canvas consists of a cotton or linen fabric stretched across a wood frame.  The artist applies a "size" to isolate the canvas from the acidic qualities of the paint.  Some artists today still size and prime a canvas with rabbit skin glue and lead white paint.  However, today most artists buy their canvases pre-sized, and then prime them with modern acrylic gesso. 

With the advent of prepared oil paint supplied in tubes in the 1800's, artists no longer had to grind their own pigments.  Artists use linseed oil or some other medium to thin the oil paints.  An thin underpainting is laid down first to tone the canvas and cover the white gesso.  The traditional layering method in oils is to work from dark to light (as opposed to watercolor where artists usually work from light to dark).  Oils are very slow to dry.  An oil painting generally takes a year to become dry enough to varnish.

My personal preferences are to use the Dutch masters' palette (muted greens/greys) and the chiaroscuro effect.  Chiaroscuro is an extensive gradation of light and dark.  This dramatic lighting tends to isolate the subject and heighten the emotional tension of the painting.