I do think the book was meant to be read by a somewhat wider audience. This could have been his ambitious life's work, but no printer wanted (or knew how to) reproduce it? The dutch in the book is quite readable even today; this is from the introduction text, written as a poem (only rhymes in dutch):
---
To the art-loving pupil
This book was written for pleasure and instruction,
for anyone who doesn’t yet know how to colour from life,
whether prints or drawings, whatever their spirit moves them to,
and who lacks nothing but proper teaching.
Come, just read this book with me; it will spark your enthusiasm,
for in it I will show you, through image and text,
what you must do to give everything, true to life,
its proper colour and character, thoroughly and correctly.
That is why this book is filled with colours,
and beside them you will find how each one is prepared.
---
To the art-loving pupil
This book was written for pleasure and instruction,
for anyone who doesn’t yet know how to colour from life,
whether prints or drawings, whatever their spirit moves them to,
and who lacks nothing but proper teaching.
Come, just read this book with me; it will spark your enthusiasm,
for in it I will show you, through image and text,
what you must do to give everything, true to life,
its proper colour and character, thoroughly and correctly.
That is why this book is filled with colours,
and beside them you will find how each one is prepared.