With zirconia, I use glaze and stain only for subtle highlight surface characteristics.  For this process, Ivocolor by Ivoclar works well on all the zirconia brands, particularly the multi ones such as Katana STML,  ZirCAD Multi, and the coming ZirCAD Prime.  This video will demonstrate the zirconia preparation required for glaze addition and then glaze/stain applications creating subtle surface enhancements.