XIXth Century French Mining engineers reports and drawings on Swansea industry: industrial spying or technological exchanges? The history of mining and metallurgical techniques during the nineteenth century is often hampered by the lack of documentation: we know today the chronology of inventions or statistics of overall production, much less the technical reality, operation, tooling, processes as administrative archives are often silent on the matter. The Paris National School of Mines (Ecole des Mines de Paris) preserves a unique collection of manuscripts of mining and metallurgical travels range from 1825 to 1909. Hundred folio collections remained inaccessible and completely untapped while school students traveled with their notebook, all around a great part of Europe and sometimes in America, specifically to get all this documentation. A few part of these precious documents have been published in the well-known "Journal des Mines" then becoming the "Annales des Mines". Most of them are nowadays an exceptional unpublished source of information about mining, ore dressing and metal processes and machineries. Was it spying or was it the dissemination of ideas and technological concepts as required by invention and innovation ? The raise of a competitive intelligence ? Some of these exceptional detailed manuscripts concerns Wales mining and metallurgy and of course Swansea copper and steel industries and trade. As the world of industrial international relationships was marked by all forms of spying, the study of some XIXth century Swansea and Welsch reports and drawings raises again the question of technological exchanges and the origin of European industrial take off set up by these global enterprises