I think you may mean the Cotinus coggygria 'Royal Purple' - if you Google image search that you will get lots of lovely pictures of it at different stages. Let us know if it's not the one and we will come up with more suggestions (or at least try to!)
Thanks Jules but that's not it. The tree I have in mind is very big, like an Oak or a Chesnut and has a lightish grey trunk and now that I think of it the leaves are perhaps more black grape coloured. I hope that is a better description.
If you cut some copper beech this time of year and place the stems in a mixture of warm water and gylcerin 9 parts to 1 you can preserve them for use all year round