Jahnson also had an extensive weapons collection, stored in Stensund Castle.
Jahnsson was hit hard by the Kreuger crash in the early 1930s, in which he was stripped of his wealth and forced to leave the Van der Nootska Palace and auction off most of the collections.
Stensund Castle was sold to Carl Matthiessen, 1933, and the weapons collection auctioned off .
The remainder of Jahnsson's collections from Van der Nootska, which mainly consisted of the Stockholmiana Collection, were donated in 1942 to the Stockholm City Museum of Axel Wenner-Gren, who in February 1938, had bought the Van der Nootska Palace.
The Stockholmiana Collection consisted of about 5000 images and about 3000 books and pamphlets.