Oil Paint
Oil paints have been used to create art since the 15th century. Most of the portraits seen in museums and public areas are oil portraits and oil is still the most popular choice of medium used for portraits today.
Oil paints are made from ground pigment (colors) that have been mixed with an oil binder to produce a fluid paint. The paints can be thinned or used straight from the tube, creating a variety of textures and fluidity. Oil paints are mainly executed on canvas (a woven cloth) made from cotton or linen. Oils can also be painted on wood or metal.
Because the finished, dry painting is solid, oils do not need to be framed under glass and only require varnish to protect the surface.
Pastels
Pastels are made from the same ground pigment as oils, but are mixed with a binder that turns them into a paste. This paste is then rolled into sticks and allowed to dry, thus leaving a pure color in stick form.( Because of this appearance, many people think they are chalk.) Unlike oils, they are a dry medium and can be used for drawing as well as fully developed paintings. They are executed on a paper or sanded board. The tooth is necessary to hold the pigment. The effect of the pigments on paper creates a luminosity that can’t be achieved with oils.
Pastels have the same longevity as oils provided they are framed properly. They must be framed under glass. For the best protection, an expert framer who uses museum quality materials should be used.
How to choose between oil and pastel
Obviously, if you have a preference of one over the other, go with with one you like the best. Oil paintings have a more fluid appearance and can have more texture. They are considered a more traditional medium and because they don’t have to be framed under glass, are not as fragile.
Pastel paintings are softer and more delicate, in most cases. There is no surface texture other than the dry pigment reflecting light. Pastel is a popular choice for children’s portraits, but can be used for people of all ages. Since they do have to be framed under glass, the size of the portrait can be a consideration.