The precious resin used by Montblanc is a modified methyl methacrylate (Plexiglas) and tolerates cleaning with water and washing-up liquid as well as, to a limited extent, low-volatile alkanes such as octane. Strictly avoid alcohols, esters (nail-polish remover), ketones (acetone), aromatics (benzene, toluene) and chlorinated hydrocarbons (trichloroethane, chloroform), as they irreversibly damage the material within a very short time. For polishing, a water-soluble diamond paste with a grit of 0.25 µm (e.g. from Winter, Hamburg) is recommended; the polish Wenol is widespread in the collector scene and recommended by many repairers, but it has no declared grit size and can wear down coatings with repeated use. Cotton cloths should be as fresh as possible because detergent residues (zeolites) can cause micro-damage; microfibre cloths and unused cleaning cloths are a safe alternative.