The natural region of Puisaye (France), situated in the north of the department of Yonne is, for France, one of the region which delivers the largest quantity of remains of iron production. During the beginning of the XXth century more than 500 000 t. of slag have been extracted to supply blast-furnace. Today, more than 2300 slag heap are known for a territory covering about 1500 km². If the localisation and the size of these heaps are known thanks to prospection realized for more than ten years (Pietak et al., 2012), little is known about the chronology and the smelting processes practiced. Since two years a new research program has started on this region in the objective to acquire dating and technical information. Two scale of study are considered. One is carried out at the scale of the natural region of Puisaye on slag heap delivering remains of slag-pit furnace. Around ten sites have been considered. Another scale of analyse concerned an area covering 2 km square situated in the north of the region, at Aillant-sur-Tholon, where around twenty slag heap are studied. On both scale, the topography of the heaps are registered. Punctual sampling of charcoal and slag are realised to acquire radiocarbon dating and technological information on the reduction processes. Surveys have been also conducted on six slag heap at Aillant-sur-Tholon, to acquire information in stratigraphy. The aim of the communication is to present the first results of this research program, showing the long aging of the iron industry which begins during the iron age (around -600/-500) and covers the roman period. During this time span, it is also possible to propose, from the typology of the waste and their association, the existence of, at least, three of four types of reduction techniques. We will also discuss the importance of this district of production in its chronological context. The condition of its development in its cultural framework in comparison with other centres of iron production known in its vicinity will also be discussed.