A high refractive index, curable, synthetic resin composition comprising a core resin composition composed of a mixture of ethylenically unsaturated compounds, and an initiation system containing both photo and thermal initiators, particularly a photochromic resin composition which further includes at least one photochromic dye. Also a curing process, which includes a combination of multi-step radiation curing and thermal annealing. Articles produced of cured composition exhibit superior physical and, in appropriate cases, photochromic properties and can be easily mass produced on a commercial scale due to short processing time and use of readily available chemicals.