The ancient bloomer process in Denmark, Norway and Sweden is examined in some detail. Bulk slags from well-studied archaeological sites have been analyzed for fourteen elements, and a database with maps generated. The slag-analytical method allows a distinction between production slags, purification slags and manufacturing slags (cinder). Furthermore it has become possible – within certain limits – to distinguish iron objects produced from Danish phosphorus-rich, but aluminium-poor bog ores from objects produced on basis of bog ores and lake ores from Norway and Sweden. It is, e.g., shown that the two Viking-age ship anchors from Ribe and Ladby in high probability were produced in Norway. A number of Norwegian iron bars from Roman iron age and medieval age are shown to be steel bars for export, and probably produced from the manganese-rich and phosphorus-poor steel ores that occur in the vicinity of Dokkfloyvatn, Oppland. Finally, it appears that many horseshoes, nails and agricultural implements in medieval time have been imported from Halland and Skane, both as finished objects and as bars (kloder og klimper) which then have been worked by the local blacksmith to acquire the final shape. Evidence of this trade of semiproducts are the purification slags (kalotter) in many Danish archaeological sites of a composition that is different from genuine Danish purification slags. Throughout the paper emphasis has been put upon the full structural and analytical descriptions of the slags and of the coexisting iron phases, including their chemical composition and hardness.