A Very Special Wedgwood Basalt Plaque

There are a lot of modern releases of George Stubbs' design of The Affrighted Horse by Wedgwood in limited editions. Most if not all of these have a flat rear surface with markings indicating they were issued in a limited edition x/xxx, and many have gold enamel markings indicating they were from the Wedgwood Collector Society. They are usually stamped Wedgwood, Made in England, as is the case with most modern Wedgwood items.

The plaque in my collection is possibly an original 18th century object, but I am having difficulty finding an exact reference. Here are the reasons that I so believe: The plaque is modeled in very high relief and the obverse surface is convex; the reverse is concave, not flat. It is marked simply WEDGWOOD in the early lettering style. It does not say England or Made in England, which would indicate 19th or 20th century manufacture respectively. There is a simple kiln mark of "0". Most unusual is the incised script title, "The affrighted horse".

Though it is possible that this is some modern release of which I'm not aware, it may be a rare 18th or early 19th century release, or possibly even a maquette created by Stubbs. I would greatly appreciate the thoughts of anybody with expertise in the area. It is a truly beautiful decorative item, but I would like to know if my thoughts on the rarity can be confirmed. As you can see from the photos, I have had it framed in a 2" thick shadow box type of frame behind Plexiglas sandwiched between a recessed matte in front and a cut out matte in the rear so the reverse markings can be read. I thought this would give it the very best in protection. Whether early, or more modern, to me it is a wonderful example of 18th century design and the Romantic movement in Georgian art.