Despite the growing number of experimental studies of fire, there is still a lack of critical information on the physical alteration of ash remains and its importance in the preservation and interpretation of combustion features in the archaeological record. This study presents an 8-year long experimental investigation of several hundreds of open fires and laboratory experiments and the analysis of their chemistry, mineralogy, morphology, and physical parameters. Important observations have been made regarding ash weathering, charcoal production, post-fire use of heated ashes, and the influence of kindling and soil organic matter on thermal alteration and reddening of the fire substrate. A wealth of information is provided on the formation of ash minerals, their physical and chemical alteration with temperature, and post-fire reactions with water. The resulting evidence can explain the recent geo-ethnoarchaeological observations that ephemeral open-air fires are likely to disappear if they are not quickly buried by sediment by a non-eroding process. Ash formed during a single or a few relighting events is extremely porous (more than 90% total porosity), light (less than 0.2 g/cm³ bulk density), and highly compressible (about 90%) under the weight of foot traffic or 1.5 m of overburden sediment. This makes ash remains extremely vulnerable to modification in an open environment and macroscopically invisible in an excavation, even in the absence of the slightest post-depositional chemical alteration. Ash remains become progressively more sintered as relighting events increase, thus producing a crusted less porous and more stable formation. Nevertheless, remains of a 5 cm-thick unaltered ash buried in a sedimentary sequence will most likely represent several tens of fires made in the same area whereas a flat 20 cm-thick ash sequence represents hundreds of fire events on top of one another. These results are of extreme importance in evaluating the emergence and use of fire in the Pleistocene and they also provide a better understanding and interpretation of ash remains in later periods. Finally, it is suggested that only a multimethod research strategy can reveal the necessary information to understand and correctly interpret archaeological ash remains.

尽管对火的实验研究越来越多，但仍然缺乏关于灰烬遗骸的物理变化及其在考古记录中保存和解释燃烧特征的重要性的关键信息。这项研究对数百个明火和实验室实验进行了为期 8 年的实验调查，并分析了它们的化学、矿物学、形态和物理参数。已经对灰风化、木炭生产、加热灰烬的火后使用以及火种和土壤有机质对火底热变和变红的影响进行了重要观察。提供了关于灰矿物的形成、它们随温度的物理和化学变化以及与水的火灾后反应的大量信息。由此产生的证据可以解释最近的地质民族考古学观察结果，即如果不通过非侵蚀过程迅速被沉积物掩埋，短暂的露天火灾很可能会消失。在一次或几次重新点燃事件期间形成的灰分非常多孔（总孔隙率超过 90%）、轻（小于 0.2 g/cm³容密度），并且在步行或 1.5 m 上覆沉积物的重量下具有高度可压缩性（约 90%）。这使得灰烬在开放环境中仍然极易发生变化，并且在挖掘过程中从宏观上看是不可见的，即使没有最轻微的沉积后化学变化。随着重新点燃事件的增加，灰烬残留物逐渐变得更加烧结，从而产生结壳较少孔隙且更稳定的地层。尽管如此，埋在沉积序列中的 5 厘米厚的未改变灰烬的残骸很可能代表同一地区发生的数十场火灾，而 20 厘米厚的平坦灰烬序列则代表数百次相互叠加的火灾事件。这些结果对于评估更新世火的出现和利用极为重要，它们还提供了对后期灰烬遗骸的更好理解和解释。最后，建议只有多方法研究策略才能揭示理解和正确解释考古灰烬遗骸的必要信息。