The OMAS Extra consists of the in-house cotton-based Cotton Resin and is therefore scratch-sensitive; polishing succeeds best with Wenol or a fine polish with small grit, in a pinch even with toothpaste. The inscription 750 on the nib denotes 18-carat gold. For renewed sealing silicone grease is used, as for example pen makers like TWSBI include with their devices or as obtainable via specialist dealers like penboard.de or US suppliers (Goulet Pens); critical sealing point is especially the feed. To clean old sealant, alongside detergent ultrasonic bath, WD-40 has also proven itself. Exact build data can be most reliably determined by direct enquiry with OMAS.