The methodological protocol developed by the C2RMF have been for now, applied on a dozen of yellow coffins from 21st dynasty of the Egyptian Antiquity Department of the Louvre Museum. This first results on different pieces of funerary set give us a preliminary view of the production and raise some questions about the manufacturing process. Indeed, the extensive battery of examinations and analytical techniques permit to identify the wood employed for the structure of the coffins, which supports the complex stratigraphy of filling materials and polychromy. These materials themselves have been determined, both pigments and varnishes, and even binders in some specific cases. The wood identification shows a large use of Acacia, with Tamarix or Palm tree for the constitutive planks and the pegs of the coffins These objects present generally the same support preparation. Directly on the wood, different layers, in nature and compositions, are applied in the way to homogenize the surface and to receive the colors. The muna, a brown Egyptian silt rich in iron and manganese used for wall preparation mixed with vegetal fibers, is first encountered. Then, a white preparation is applied in one or sometimes two layers and contained principally calcium carbonates, or double carbonates, calcium and magnesium, which have been identified in particular cases. This coffin production is characteristic by the colour of it background which confers this particular aspect intended to imitate golden royal coffins. The study of the corpus permit us to highlight that the application of the yellow background is more complex than thought and actually depends on the part of the coffin studied. Difference of treatment have been seen between the inner and the outer part of the case and also the higher and lower part of mummy boards and lids. Concerning the polychromy we found that all the materials used are generally quite the same on the objects studied. We encountered iron yellow and red, orpiment, Egyptian blue and copper green. This last colour posed some problems of identification. Results revealed the presence of a synthetic copper green (bronze scraps traces) currently degraded which can be sintered pigments (close to Egyptian green) and organometallic pigments (copper-protein complex). The bright yellow varnish, also responsible to the golden appreciation, have been identified by GCMS campaign to be mastic resin, an exudate from Pistacia, and its application depends here also of the part of the funerary set studied. Orpiment grains can be encountered trapped in this last surface layer, or elsewhere in the stratigraphy, enhancing this shiny effect. We are trying to identify its real position in the stratigraphy for each coffin, in case it can be a workshop marker.