The invention relates to a process for preparing a dry film resist by forming a photocurable resin composition onto a support film with a thickness of 1 to 50 .mu.m and optionally laminate a protective film onto the photocurable composition layer to obtain a dry film resist; whereby the photocurable resin is formed from a homogeneous mixture comprising (a) from 20 90 wt % of an alkaline soluble binder oligomer or polymer; (b) from 5 to 60 wt % of one or more photopolymerizable monomers which are compatible with the oligomers and polymers of component (a); (c) from 0.01 to 20% by weight of one or more photoinitiators; (d) from 0 to 20% by weight of additives and/or assistants; and (e) from 0.1 to 10% by weight of a leuco triphenylmethane dye of the formula (I), wherein R.sup.1 is a residue selected from (II), R.sup.2 is C.sub.1 C.sub.12 alkyl or phenyl which may be mono-, di- or tri-substituted by C.sub.1 C.sub.6 alkyl, trifluoromethyl, C.sub.1-6 alkoxy, C.sub.1-6 alkylthio, halogen and nitro; R.sup.3 is hydrogen or C.sub.1 C.sub.12 alkyl; R.sup.4 to R.sup.9 independently of one another are hydrogen or C.sub.1 C.sub.12 alkyl; X is O, S, NH or N--C.sub.1 C.sub.12-alkyl; (a) to (e) being 100% by weight. The above composition is useful to avoid unfavourable colour generation during the heat lamination ##STR00001##