Conversation so far:
What was Jan van Eyck's maturity?
The years between 1434 and 1436 are generally considered his high point when Jan van Eyck produced extraordinary works and really matured as an artist.
What was one of Jan van Eyck's successes?
The years between 1434 and 1436 are generally considered Jan van Eyck high point when he produced works including Lucca Madonna and Virgin.

Question: What was special about it?
Self-contained rewrite: What was special about Jan van Eck's successful paintings?