Pepin Press in the Netherlands has issued a number of high quality artists books for multi-media, including watercolor.  The paper weight is less than 90 lbs, so it is not possible to scrub out mistakes too vigorously without making a hole (this is the voice of experience).

I used these to get back into practice after an almost 15 year break from any serious work. They are also a great place to try out new techniques, mediums, brushes or anything else that you might not want to introduce immediately into a more formal piece of work.

A number of the images in this particular volume are part of the collection of the Rijksmuseum in Amsterdam.

An interesting project hosted by the New York Academy of Medicine is Color our Collections which provides free downloadable coloring sheet from more than 100 institutions worldwide: colorourcollections2019.

For more information on this project, please see My Modern Met: “Over 100 Museums Invite You to ‘Color Their Collections’ with Free Adult Coloring Books.”