On old Meisterstücks, the barrel typically consists of celluloid, the other parts of hard rubber. Hard rubber can carefully be rubbed with olive oil; light spots thereby become darker and the appearance evens out. Polishing reliably removes adhesive and discolouration residues but can also wear off fine embossings like nib-width statements or model designations. Anyone wishing to avoid the risk should hand the writing instruments over to a specialist (e.g. Horst Schrage, maxpens.de), who can gently freshen them up.