As Cook and Wedderburn note in the index to the Library Edition, Ruskin often conflated the Dutch and Flemish schools of painting (see under 'Dutch' in Works, 39.171). Thus remarks which specify one school apply equally to the other. Such remarks are also confined, almost exclusively, to artists of the seventeenth century, commonly considered the Golden Age of painting in the Low Countries. Ruskin tended to write negatively of these artists. He perceived in them a preoccupation with mechanical imitation at the expense of other, and higher, aims. Where they attempted to follow nature, they could be truthful and instructive, and occasionally reproduce some beautiful elements of the environment, such as clear, cool skies ( MP I:207), winter effects ( MP I:281), and 'pure and silvery and luminous' architecture ( MP I:110). But they generally concerned themselves with the redundant detailing and cold, incorrect representations of mundane subjects. Ruskin was particularly damning of those who painted marine subjects (see Ruskin and Dutch marine painting). His chief exceptions were Rubens and, to a lesser extent, Rembrandt and Van Dyck. Rubens produced 'the first instances of complete unconventional unaffected landscape', while all three comprised 'the northern parallel to the power of the Venetians' ( MP I:89). Ruskin's later criticisms (in Modern Painters V and elsewhere) of Dutch and Flemish painters, including Rubens, emphasised their immoral and unspiritual nature.