The fields of old Persian pieces are lavishly covered with intricate designs of buds and blossoms supported by vines and tendril, and frequently encircled by arabesques that interlace so as to form a harmonious whole. Modern pieces frequently have a solid color field with central medallions and triangular corners defined by graceful lines. The field is often covered by realistically drawn or conventionalized floral designs that are arranged with studied precision. Surrounding the fields are several borders containing undulating vines with pendant flowers or palmettes coordinated in design and color with the main pattern. It is in, however, the colors, which are delicate yet rich, subdued yet lustrous, that these Iranian rugs surpass all others. Their most distinctive tones are blues, reds, browns, and greens so arranged that the ground colors of border and field generally contrast, yet remain in near perfect harmony. On some city Persian carpets a central motif or medallion is sometimes omitted and instead an all-over design of repetitive floral icons is adopted. To attain the fine and beautiful curvilinear designs common to Persian rugs, the intensity of knots must be increased. Where a tribal rug may have 80-100 knots per square ” (KPSI), a Persian City carpet could have 200-300 KPSI, allowing the closely spaced knots to create a visually curved line. Tribal carpets, on the other hand, usually use geometric designs which are easier to achieve with wider spaced knots.