The Royal House of Norway has a large furniture collection from the 19th century. Most of this historical furniture is coated with shellac, which was frequently used for such a purpose in the same period. Since these objects are part of the royal collection, they are still in daily use at the different residences. The furniture, therefore, needs a more frequent (and, probably, aggressive) cleaning than what is common for museum objects. For this reason, the effect of three different cleaning products used at the royal collections on shellac-coated mahogany was investigated for the first time. A thorough study with non-invasive methods (portable FTIR spectroscopy, colorimetry, glossimetry) was undertaken to investigate whether the chemical composition, the gloss and the colour have been altered after the cleaning of varnished wood with the selected cleaning products. The investigations were done on fresh and aged mahogany wood samples coated with shellac. The results of this study show that one of the cleaning products probably causes chemical changes in the shellac. This study provides information for the ordinary cleaning and subsequent conservation treatments of the above-mentioned collection and aims to create a preliminary non-invasive protocol for investigating varnish-coated wood.