Since the first developments of anthropogenic lime materials radiocarbon (14C) dating in the 1960s, numerous studies have been undertaken and developed to investigate the topic further. Historic mortars are complex composite and open system materials that can incorporate a large range of components. Due to the complexity of the historic lime mortars composition, they are not part of a routine protocol in most radiocarbon laboratories and reliable dating is not always achieved. A thorough characterization needs to be performed and different preparation methods can be considered as a function of their compositions. A vast range of terms are employed to qualify the lime mortars components and alterations that can possibly have an influence on the dating result. Here, a detailed description of these components and the various terms used is listed. To illustrate this, images obtained by thin-section petrography and cathodoluminescence are presented in addition to radiocarbon results using stepwise acid hydrolysis on Belgian mortars having different provenance, state, age and composition. Depending on the type of aggregate used, the type of binder and its conservation state, the eventual presence of weathering carbonates and the assumed speed of the carbonation process, the reliability of radiocarbon measurements using the stepwise acid hydrolysis technique is discussed and confronted with presumed historical constraints.

Commercial bentonite from the Kopernica deposit, Slovakia, is currently mined by the CERTECH Company, Poland, to produce materials intended for animal-care applications and other industrial purposes. The present study aimed to assess the mineralogical, petrographic and physicochemical characteristics of three bentonite varieties from Kopernica used by the company. The X-ray diffraction, optical microscopy, field emission scanning electron microscopy (FESEM), nuclear magnetic resonance, thermal analysis, infrared spectroscopy and chemical analyses showed that the main component of the rocks is montmorillonite with the average structural formula Ca0.31K0.08Na0.04(Al3.23Mg0.54Fe0.23)[(Si7.80Al0.20)O20](OH)4. In addition, opal-C/CT, biotite, potassium feldspar and plagioclase, quartz, clinoptilolite and kaolinite are present. Key information about the textural relationships between the mineral components identified was obtained from detailed thin-section petrography and FESEM studies. The rocks studied have fragmented, eutaxitic texture. They are composed of pumice fragments collapsed into lenticular masses (fiamme) which were strongly deformed and altered, though the shard structures were retained. The compressed glass shards were moulded around pyroclastic grains such as crystal fragments of quartz, biotite and zoned plagioclases, and clasts of volcanic rocks. Observations by FESEM showed that the axes of shards and the walls of the flattened vacuoles are outlined by the inward-growing microlites of silica (axiolitic texture), whilst the interiors of shards are altered to clay. Grain-size distribution, textural properties and microscope observations of grain-size fractions reveal that the Kopernica bentonite contains montmorillonite-opal aggregates difficult to disperse in water.