BLH, mr.T gave me the link to your post at engravers forum.
I have to say there is very good book about Russian arms by Juri Shokarev "Russian Hunting Arms. Makers and Firms", 2005
In this book the author tells short story about hunting arms development since Russia very beginning. There are some photos of Russian made guns from most Russian museums such as "Moskovsky Kreml'", "Orudjeinaja Palata"...
Aprx. 1000 (!) names of Russian makers, firms and factories since 17 till early 20-th century.
There were hundreds of engravers in Russia of very high level, unfortunatly we lost most of these names and remember foreign names mostly such as Faberge and only just because Tsars loved him.
But let me remind you, that all Faberge stuff been made by Russian jeweller and engravers hands, but not by Mr. Faberge personally.
Re. this Matska-Lebeau gun. I know now how to get an access to the gun and will tell about my reseach very soon.
But what I have to say now, if this gun is really Lebeau gun and it was in white (I don't see any other reasom of Matska name on locks) and been finished and custom tuned by Matska, 99% that engravings been made here in Russia and probably by unfortunatly one more unknown Russian engraver.