A process for printing an image on a substrate comprising applying thereto a composition comprising a liquid medium and a compound of Formula (1) A-N=N-L-N=N-A wherein: each A independently is optionally substituted aryl or heteroaryl; and L is an optionally substituted, optionally metallised 1,8-dihydroxynaphthylene group; provided that: (i) at most one of the groups represented by A has a hydroxy substituent ortho to the -N=N- groups shown in Formula (1); and (ii) Formula (1) is not: Also claimed are compositions for printing, compounds and processes for making the compounds.