The influence of the type of photoinitiator, type of polymerizable reactive diluent and added amine synergist on the yellowing which occurs during the curing of clear films is examined. Type I photoinitiators based on acetophenone give rise to the least yellowing. The presence of amines, such as N-methyldiethanolamine, increases yellowing to a noticeable extent. Amino groups present in the initiator or the reactive diluent lead to marked yellowing. The chemistry responsible for the yellowing is explored.