pigmented colorants: dependence on media and time - Cornell ...

stance has dried. This behavior is desirable when an artist wants to rework an
area that was completed previously. However, the resulting paint film is not very
permanent nor durable, as it is sensitive to moisture and quite brittle.
A great number of plant gums were used in different times as binders. The
most common is the material gum arabic, which comes from a particular variety of
the accaia. Accaia was one of the few trees that grew in ancient Egypt and served
as a binder in that period. Gums have similar behavior to that of honey; it is re-
workable and the dried film results in a matte surface. Gum arabic is the primary
ingredient for watercolor painting. Other watercolor additives that are sometimes
included are a plasticizer, usually glycerin, to soften the dried gum arabic and help
it re-dissolve; and a preservative, to suppress the growth of mold and bacteria.
The method of mixing watercolor paints with an opaque white pigment is tra-
ditionally referred to as gouache. Gouache is an opaque watercolor paint, and
creates a flawless, flat color area. Watercolors are layered in glazes, while gouache
is applied more directly, since applications of gouache will completely hide the
layers underneath. Whereas, the white of the paper provides the light for water-
colors (those who practice watercolor typically do not use white), the brilliance of
gouache comes from the pigment. The perfection of the gouache surface appeals
to illustration and commercial artists. Projects on both binders can be completed
quickly, as gum arabic dries rapidly.
2.3.2 Protein-Based
Proteins are compounds that consist mainly of carbon, oxygen, hydrogen and
nitrogen. Similar to carbohydrates, proteins are also comprised of building blocks.
There are approximately two-dozen naturally occurring amino acids known, which
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