At the beginning of the 1950's, Cox starts experimenting with making multicolored prints on his own litho-press.  Le fou rire du nouveau riche is one such work, and the M HKA collection contains several printer's proofs of this lithograph.  Feeling limited in his printing technique and not wholly satisfied with the results, in 1952 Cox decides to call on the celebrated Parisian printing atelier of Mourlot.  Here he could realize his color litho's in ideal conditions, and profit from this workshop's accumulated experience - as did fellow artists like Bernard Villon, Marc Chagall and Alberto Giacometti. 

This collaboration resulted in some wonderful works such as Verhuizing ’s avonds (1952), Vreugdetakken (1952) and the portrait of his girlfriend Yvonne: Verrassing [Sursprise] from 1952. 

In 1953 Cox exhibits a selection of his lithographic work in Amsterdam.  This exhibition later also traveled to Indonesia, and a companion catalogue was published with texts by J.H.W. Veenstra.