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Ternary Systems. Illustrating equilibrium conditions for three-component (ternary) systems in two dimensions is more complicated than for binary systems. One option is to add a third composition dimension to the base, forming a solid diagram having binary diagrams as its vertical sides (see figure). Here, boundaries of single-phase fields (liquidus, solidus, and solvus lines in the binary diagrams) become surfaces; single- and two-phase areas become volumes; three-phase lines become volumes; and four-phase points, while not shown in the figure, can exist as an invariant plane. While three-dimensional projections can be helpful in understanding the relationships in the diagram, reading values from them is difficult. Ternary systems, therefore, are usually represented by views of the binary diagrams that comprise the faces and two-dimensional projections of the liquidus and solidus surfaces, along with a series of two-dimensional horizontal sections (isotherms) and vertical sections (isopleths) through the solid diagram.