A trawl through the advertisements in this topic:
http://www.925-1000.com/forum/viewtopic ... 38&t=20661" onclick="window.open(this.href);return false; show that David Andersen was using the spelling as 'Christiania' as late as 1907, whereas J. Tostrup was using the spelling 'Kristiania' in his earliest shown advertisement 1884. Andersen's advertisements however are in English, and this may be the reason for the earlier spelling. Perhaps, as he was exporting great quantities of his work, he retained the more widely known spelling of the name.
Trev.