This is indeed vey difficult to distinguish. There is not a great production in Japan - so it is more likely to be from Bohemia or Italy. The technique is Terzo Fuoco - as it needs to be fired three times, once for annealing the glass, once for fixing the raised enamel, and once for the gold. It requires a very close temperature control. The largest Italian maker was Barbini of Martelago - usually the decoration is a little more elegant. But indeed, Borske is the largest.