The Baker interference microscole was successfully used to observe and measure some of the optical properties of external skin layers on cellulose acetate, modified acrylic, and polyester fibers. The skin on cellulose acetate was shown to he composed of normal acetate with void inclusions of 13% to 17% of the total volume. Optiral measurements on polyester fibers revealed the relationship between indices of refraction, birefringence, and draft ratio. The rubber phase in ABS plastics and emulsions was observed and compared. In addition, particulate matter unobserved by other means was found in other solutions.