Just to add more to the mystery, Leopold, Count von Thun und Hohenstein was Austrian and in the Austrian section of Warren's link above, the exact crown can be seen as on the porcelain being an Austrian "crown of nobility".
So, IF I'm correct, the item could have been made at the factory Osipi has mentioned.
There are a couple of issues here. We should be careful in distinguishing the mark on the porcelain as the cypher of the original owner whereas the maker's mark would appear on the bottom of each piece. It's quite possible that the Graf von Thun und Hohenstein commissioned a set from the family factory and it is his personal cypher that we see. However, Graf Leopold's full Christian name was Leopold Leo so in theory at least his cypher
[thumbnail 1] should consist of the stylised letters LLTH. Individual elements of cyphers can be hard to distinguish at the best of times but even so (and while acknowledging that anything is possible) I'm not sure that a sustainable argument can be made for LLTH appearing on the porcelain.
The other and perhaps more telling issue concerns the coronet. All male members of the Thun und Hohenstein family were made Reichsgraf - Counts of the Holy [Roman] Empire - in 1629. They were thus entitled to display the 'Older Crown of Counts' [five strawberry leaves]
[attached image 1] rather than the 'Older Crown of Nobility' [three strawberry leaves separated by two pearls]
[attached image 2]. The latter would more likely have been used by old non-titled noble families and old families whose titles weren't granted at the Imperial level. It is hard to imagine that a member of a proud Imperial comital family would forego the use of their rightful insignia which denotes their rank within the aristocratic hierarchy in favour of insignia denoting a lesser rank.
The coronet that started this investigation closely resembles the HRE Older Crown of Nobility and later Austrian Crown of Nobility
[attached image 3], neither of which, logically speaking, would be used by an Imperial Count such as a Graf of the House of Thun-Hohenstein. A further argument against a Thun-Hohenstein cypher incorporating the Austrian Crown is that the Empire of Austria did not come into being until 1804. A family which had been granted its highest rank by the Holy Roman Emperor would not readily give that distinction up.
There are always exceptions to every rule of course and logic does not necessarily apply, but the probability is that the personal cypher of a Graf of Thun-Hohenstein would display the HRE Older Crown of Counts. That coronet is quite different to the coronet depicted on the porcelain.
↓ The original and as yet unidentified cypher
↓↓ 1. Holy Roman Empire Older Crown of Counts
....2. Holy Roman Empire Older Crown of Nobility
....3. post-1804 Austrian Empire Crown of Nobility
