Microbial biofilms have developed on the surfaces and within the painted and gilded layers of mummy cartonnage at the Saqqara museum storeroom in Giza, Egypt. SEM–EDX, XRD and FT–IR–ATR techniques were applied to analyse the coloured and gilded materials, ground layer, textile support and binder used for the cartonnage. Aspergillus niger (24.8%), Penicillium chrysogenum (21.5%) and a novel cartonnage‐biodegrading bacterium, Bacillus sonorensis (23.7%), were the most abundant microbes growing over the cartonnage surface. In addition, Aspergillus tamari (15.4%), A. fumigates (8.1%) and Fusarium solani (6.5%) were identified. The pigments comprised Egyptian blue (cuprorivaite), cinnabar (red), orpiment (yellow) and green pigment made from a mixture of cuprorivaite and orpiment. Gold leaf was used for the gilded layer, calcium carbonate and gypsum comprised the ground layer, gum arabic was the binding medium and the fibre base was a fine linen textile. Microbial colonization tests were performed on aged cartonnage replica samples made from linen and pigments of similar composition to ancient pigments found in the cartonnage. Each sample was inoculated separately with A. niger, P. chrysogenum and B. sonorensis. Yellow orpiment samples were the exception, as no colour change was detected after colonization by the examined micro‐organisms.

A wooden coffin lid, of unknown provenance, with ground and colored layers and an ancient textile, was found at the Egyptian Museum basement in Cairo (JE 36806). The information obtained leads to the conclusion that the coffin lid dates back to the Ptolemaic period in Egypt (332-30 BC), whereas the textile does not belong to the coffin lid. Portable x-ray radiography, photography, optical microscopy, reflected light USB microscopy, Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Raman spectroscopy were used to assess the deterioration and the structure of the coffin lid and to understand how it was made in the necropolis workshop.

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