NOVELTY - Forming a crystalline ribbon involves providing a mesa crucible (1314) having edges (1304) defining a boundary of a top surface of the crucible, forming a melt of a source material on the top surface, and pulling a crystalline ribbon from the melt. The edges of the melt are retained by capillary attachment to the edges of the mesa crucible.    USE - The method is used for forming a crystalline ribbon for use in making solar cells.    ADVANTAGE - The invention provides a lower cost and high quality substrate materials for making solar cells.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (a) an apparatus for forming a crystalline ribbon, which comprises a mesa crucible having edges defining a boundary of a top surface of the mesa crucible;    (b) a method of controlling temperature of a mesa crucible while forming a crystalline ribbon, which comprises positioning an insulator comprising movable elements along a mesa crucible, disposing the mesa crucible in a furnace, and creating controlled heat leaks by moving the movable elements of the insulator relative to the mesa crucible;    (c) an apparatus for controlling temperature of a mesa crucible while forming a crystalline ribbon, which comprises a mesa crucible, an insulator comprising movable elements along the crucible, and mechanism for moving the movable elements of the insulator relative to the mesa crucible to create controlled heat leaks;    (d) a method of replenishing a melt of a source material on a mesa crucible, which comprises distributing a source material onto a mesa crucible, thus reducing the heat load required to melt the source material; and    (e) an apparatus for replenishing a melt of a source material on a mesa crucible, which comprises mechanism for distributing a source material onto a mesa crucible.    DESCRIPTION OF DRAWING(S) - The figure is an isometric view of a graphite mesa crucible for growth of ribbons.    String introduction holes (1302)    Edges (1304)    Cutouts (1310)    Mesa crucible (1314)    Flat (1318)