The blue, diamond-shaped vase in the De Witte Zwaan collection is decorated using the intercalary, or acid-etching, technique. This process applied the decoration both between the layers of glass and on the surface. This created a stunning sense of depth in the glass. By playing with colors and alternating rough and smooth surfaces, the Daum factory transformed such a small vase into a true work of art. The artists at the Daum factory always signed their work with the name Daum Nancy, often accompanied by a Lorraine Cross. Here too, the signature can be found on the side of the vase. Acid-etched glass is a type of annealed glass treated with hydrofluoric acid to give the glass surface a matte appearance.