Nice and interesting flower - and very well grown plant!
The whole concept of P. barbatum var. nigritum seems a bit confused...but Braem mentions that the type specimen of the plant, published by Reicbenbach fil. as Cypripedium nigritum, has been found to match the type of P. barbatum and thus is considered to be synonymous. As I understand it, P. barbatum var. nigritum is now only used as a horticultural epithet or in trade to describe a darker coloured form of P. barbatum - and thus not, botanically, treated as a separate taxonomic entity.
In P. barbatum, again according to Braem, only the superior margin of the petals are "ornamented with small, near-black maroon spots" - and the margins of the petals are ciliate (whether this is the case with your flower, is a bit difficult to ascertain due to the background). And it might seem doubtfull, whether the staminode shield of your flower does match Braems description, too: "The staminodal shield is horseshoeshaped ... The apex shows lateral, falcate, acute teeth and at the centre of the apical margin there is a third, much smaller tooth"?
Might that gorgeous, bronze hued flower have a hybridic background?
Kind regards,
Jens