I’ve owned a facsimile of Owen Jones’ study of ornamental design for many years. Jones was an architect who helped in the planning of London’s Great Exhibition in 1851, and in the subsequent development of the Victoria & Albert Museum. The Grammar of Ornament (1856) originated from this work, a lavish guide to the history of ornament through the ages, and from all parts of the world. My facsimile is a large, heavy and unwieldy volume: nice to look at but difficult to use. One of the earliest posts here linked to an online copy but a recent addition to the archives at the University of Heidelberg is better quality, and also much more accessible.
What I’m hoping for now is that someone will do the same for Auguste Racinet’s Polychrome Ornament (1877), a book inspired by The Grammar of Ornament‘s example which is even more lavish. This Flickr set has copies of the plates but when anything at Flickr can be deleted on a whim it’s always better to have an alternative available.