Lightly oil an 8 by 12 by ½-in/20 by 30 by 1-cm frame and place on an oiled marble.
Combine the sugar and water in a heavy-bottomed saucepan and bring to a boil, stirring constantly. Stir in the glucose syrup and cream of tartar and, if using, add powdered or liquid coloring as desired. Return the syrup to a boil.