Age-metallicity relation for clusters studied in this work. Upper and lower panel show linear and log-age, respectively. Clusters with ages derived using Dartmouth isochrones (black squares); clusters with reliable number of stars for metallicity determination having ages derived from the Padova isochrones (open squares); clusters with 1−4 stars for metallicity calculation with the Padova ages (open circles). Red dots indicate clusters for which metallicity was determined for the first time. Overplotted are theoretical models: PT98 bursting model (solid line); PT98 closed box model (gray dashed line); C08a (yellow dash-dotted line); HZ09 model (green dotted line); R12 (turquoise dashed line); PG13 (black dash-dotted line); M14-0, M14-1, M14-2 (magenta dashed, dash-dotted, dotted lines, respectively); P17 (blue solid line). Grey, shaded area marks ages older than the adopted age of the Universe (13.8 Gyr).