From their website:

We are creating a free online database of documentary watercolours painted before 1900. For the first time, you can explore these fascinating visual records on a world map, search for topics that are important to you, and compare watercolours from multiple collections in one place. We hope that this project will not simply preserve the watercolour record but revive it, sparking new conversations and revelations. By making history visible to more people, we can deepen our understanding of the world.
We are a UK-based charity, but the project is truly global. We work with private and public collections from around the world to locate and publish their images, many of which have never been photographed before.There are thousands of watercolours still to add. If you think you can contribute, let us know.

For more information, click here