The Pristine survey is a narrow-band , photometric survey focused around the wavelength region of the \ion CaII H & K absorption lines , designed to efficiently search for extremely metal-poor stars .
In this work , we use the first results of a medium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars ( \textrm { [ Fe / H ] } \leq - 3.0 ) in the Pristine survey .
We consider methods by which stars can be selected from available broad-band and infrared photometry plus the additional Pristine narrow-band photometry .
The spectroscopic sample presented in this paper consists of 205 stars in the magnitude range 14 < V < 18 .
Applying the photometric selection criteria cuts the sample down to 149 stars , and from these we report a success rate of 70 % for finding stars with \textrm { [ Fe / H ] } \leq - 2.5 and 22 % for finding stars with \textrm { [ Fe / H ] } \leq - 3.0 .
These statistics compare favourably with other surveys that search for extremely metal-poor stars , namely an improvement by a factor of \sim 4 - 5 for recovering stars with \textrm { [ Fe / H ] } \leq - 3.0 .
In addition , Pristine covers a fainter magnitude range than its predecessors , and can thus probe deeper into the Galactic halo .