The 15th century in Dutch painting was that transition period when perspective was not quite understood yet (or maybe just not deemed relevant), painting styles were still iconic rather than realistic and subject matter was almost exclusively religious. What little survives of this 'church art' today - after the Reformation Iconoclasm - is brought together from museums around the world in the Dutch Primitives exhibition at Boijmans van Beuningen.
The interesting thing about this period is to see 'primitive' painters (in Dutch the exhibition is just named 'Early Dutchmen') on the brink of discovering new ways of painting. Perspective, for instance, is clearly better understood by some painters than others. Less than a century later, it would be a sine qua non of Renaissance art. Another example is portraits, which at that time are more like icons - idealized, expressionless, devotional - but which some painters start treating in a different way. They start adding expression to faces, painting real people instead of religious ideals.
One of the most sophisticated artists of the period is Geertgen tot Sint Jans. Not much is known about him, except that he worked in Haarlem, at the monastery of the Knights of Saint John (hence his name), in the second half of the 15th century. While in some respects his work is indeed primitive, especially in his oval, doll-like faces, it also shows a peculiar sensitivity. The forlorn figure of 'John the Baptist in the Wilderness' ('Johannes de Doper in de Wildernis'), for example - whose wilderness looks more like a romantic garden - has a kind of naive charm which would disappear in the self-consciousness of Renaissance art.
Worth a visit, if only for his masterful use of colors, so vivid they still dazzle five centuries later.