Abstract: A rotatable cuvette array made of PETG plastic for mixing two substances has a circular lower section with a number of circumferentially spaced cuvettes each having inner and outer compartments, both of which have upwardly diverging walls, and a ramp separating the two compartments. The edges and corners of the cuvettes are rounded to provide additional strength through increased thickness at those points. The upper section of the cuvette array is a disc having alternating opaque and transparent portions providing optic pathways through only the outer compartments of each cuvette. The upper section also includes a number of holes which provide access to each inner and outer compartment of each cuvette for filling. The upper and lower sections are separable to permit cleaning and subsequent reattachment so that each cuvette array is reusable.