Among many others, Schönberg employed smooth, glazed, and matt writing paper; yellowish, rough-surfaced drawing paper; watermarked bond paper; linen-faced writing paper; and transparent tracing paper. Schönberg rarely used charcoal or black chalk. In their natural form these can be unambiguously distinguished by sight, through their material characteristics and the type of mark they make. However, because by the early 20th century both had already for a long time been commercially available in many different grades, combined with additives and pressed into pencils, and because the mark they produce can be compacted and intensified or faded by surface wear, they can be difficult to differentiate. The portrait drawing represents the wife of the artist.