Apparently an alteration of Italianzincozincn. (1730 or earlier).
Meaning & use
Obsolete. rare.
1743
Zinc.
Apparently only used in the correspondence cited in the quots.
1743
He [sc. Carlo Ginori, Italian porcelain manufacturer] talks to me much about cobalt and zingho, two minerals which he says are found in England, and which would be vastly useful to him in composing the colours for the painting his China.
H. Mann, Letter 12 March in H. Walpole, Correspondence (1954) vol. XVIII. 184
1743
He promised me too to go to Lord Islay to know what cobolt and zingho are.
H. Walpole, Letter 10 June in Correspondence (1954) vol. XVIII. 250