Described herein is a cast-molding process for producing contact lenses in a relatively-short curing time from a lens-forming composition, which comprises (a) at least one thiol-containing compound or component, (b) at least one metal scavenger, and (c) at least one free radical scavenger and which has a pH of from about 2.5 to about 5. The addition of a chain-transfer agent into a lens-forming composition can reduce not only the curing time of the lens-forming composition but also reduce the elastic modulus of resultant crosslinked materials (e.g., contact lenses) from the lens-forming composition. The lower pH and the addition of metal scavenger and the free radical scavenger into the lens-forming composition can ensure that the lens-forming composition to have a shelf life of at least three days.