For anyone interested in the topic of the lamination material, the effects of adding varying amounts of Mo changing the annealing completly etc :Thyssen-krupp published a nice overview about soft magnetic alloys:
http://www.thyssenkrupp-vdm.com/fileadmin/Downloads/Broschueren/pdf/VDM_Report_27_english.pdf
also google for the term "the permalloy problem" if you want to dig deeper.
Over the years Neumann used UI30/25 lamination of Garantie A-50, A-51 and A-52 for the production of their mic transformers.
The colour of the laminations depends on the annealing process, the older Garantie A-50 uses oxidation at a certain temparature point during the heat treatment, setting the dark hue.
Here is a pic of various laminations.
The first two rows are all original VAC UI30/25 lamination, Some of them are made from the same material but heat-treated differently.
Third row left shows two different UI30 (non-25) laminations with four holes. Short-cutting the two legs makes it usable for UI30/25 use.
Third row right shows currently made Magmet 375 UI material already cut to size.