Ruby red cup with oxide film, probably Ilmenau technical school

Small cup made of ruby red glass, blown in front of the lamp, slightly iridescent surface with a fine silver-grey oxide film, body with thickened rings and mouth edge with a melted profile. Cup is in intact condition. Height: approx. 6.0 cm, diameter: approx. 4.0 cm. Mug is strongly reminiscent of designs by Karl Koepping. probably Ilmenau technical school and training workshop around 1900