These are two blade cores from Moravany Banka (Late Gravettian at 22 k.a BP) in Slovakia. Both were broken and the fragments which were found in short distance to each other were glued again. While the fragments of the first core, show similar patination, the patination of the fragments of the second core, although prepared at the same time, is quite different.
The surfaces of most flint artifacts show changes through a process known as patination. Patina color and thickness is dependent on age but also on the microstructure of flint, its permeability, the kind and distribution of flint impurities and the microenvironment of the soil, where the artifact was embedded.
White patina refers to a thin layer of whitish coloration covering the surface of an artifact. Most authors agree that it is induced by alkaline environments. Rottländer mentioned a pH of >10 as one major prerequisite.
Color patinas, also present in the artifacts shown here, are generally explained as being a deposit of various minerals present in the groundwater. Already patinated surfaces seem to be more prone to this effect, due to their increased porosity. Another explanation could be that metals /pigments like iron are already part of the flint matrix and oxidize at the surface. Alternatively peat may cause a yellowish-brown patina on some artifacts.
Surface findings or series of artifacts from old collections with unclear stratigraphy were often arranged according to the grade of their patination. One prominent example for this method is the wonderful book of F Bordes: “Les limons quaternaires du bassin de la Seine” from 1954. Such arrangements have to be reviewed with very great care and may be extremely misleading. Using this method, a different age would be ascribed to different parts of the second core shown in this post, whose fragments were certainly contemporaneous but embedded in different microenvironments.
Serie blanche from Tillet, from: “Les limons quaternaires du bassin de la Seine”