I have seen numerous articles referring to the early twentieth century as the Golden Age of Illustration but for me the first true age of illustration lies in the 13th, 14th and 15th century. Then there seemed to be that necessary combination of skill knowledge and resource to produce great books and the required personal wealth and vanity to support their production.
The Luttrell Salter which is in the British museum is an example I have mentioned before.
Recently another excellent example of this kind of illustration came up for auction in Sothebys.
It was Louis De Gruuthuse's Copy of the deeds of Sir Gillion De Trazegnies in the Middle East (1464). The 237 page boasts numerous illustrations but for me the borders of these pages are where the magic is. Of the pages reproduced were intricately worked foliage. Among the foliage are depictions of small cannon, peacocks, men with swords and a monkey pretending to be a doctor examining urine in a jar. It is reasonable to speculate some of these at least were for satire and amusement.
The estimate for the auction was 3-5 million dollars. It would have been a pity for such a book to disappear into a private collection. Happily the book has been bought by the Getty Museum. It went for 6.2 million dollars.
The J. Paul Getty Museum has a great resource here looking at renaissance manuscripts.