Offset of [Fe/H] with respect to the median MZ_*R, Δ[Fe/H]_bulges, as a function of the difference between the two formation times, T₅₀ and T₇₀. We show the secondary dependence of the offset on the f_acc (right panel), and f_{ex − situ}, defined as the sum of f_acc and the fraction of DB stars (left panel). The separation in fast and bursty formation history is given by a threshold in T₅₀ – T₇₀ ∼ 1 (red vertical line).