Isochrones for an age of 12 Gyr and [Fe/H]  =  −1.61, under various assumptions about the metal mixture and the initial He abundance. The CNONa-MgAl label denotes the mixture with the C-N, Na-O and Mg-Al anticorrelations, and Y = 0.246; (CNO)_enhNa denotes a mixture with C-N, Na-O anticorrelation, and the CNO sum enhanced by a factor of two with respect to the FG mixture – as in 42 – and Y = 0.246; (CNO)_enhNa,He − rich denotes the same mixture as the (CNO)_enhNa case, but with Y = 0.40. Filled circles mark selected points along the isochrones for which we show in the following the corresponding synthetic spectra.