Most old masters here in the Netherlands didn't glaze. Glazing is one of the most misunderstood aspects of painting I think. There is the so-called 'glazing-myth'.
The dutch old masters relied on the proper mixing of the colours to achieve their effects. 'Glazing' can destroy a well-painted passage. (And I have some experience in wrongly applying glazes
)
What they did sometimes was to mix retouching varnish with pigment, so you get a very thin transparant layer. It's a bit like watercolour.
Hope this helps,
Greetings,
Peter