Fraction of white dwarfs with calcium absorption (ƒ_Ca) as a function of the effective temperature (T_eff). The J-PLUS model and its 68% confidence interval are shown with the purple line and area, respectively. The squares show the fractions derived from the 40 pc sample for three different tiers with increasing sensitivity to the presence of metal lines (see text for details). The pentagons are the fractions estimated with the SDSS DR16 spectra gathered in the GF21 catalog. The dashed line depicts the J-PLUS model with an addition of 0.06.