Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide.  is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide () and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula ().