A visitor has sent me these two images, one of an ancestor Reverend Henry Purcell which the family generously gifted to the Gibbes Museum in 1989.
However, the visitor is keen to know more about the second miniature portrait, although in their research so far little has been established about it.
The portrait is on porcelain and depicts a man with a robe and chain. It is 45mm x 34mm in size.
The portrait has been shown to a number of art experts, but seemingly with little success.
Unfortunately, I have not been able to assist very much either and so have replied to the owner as follows;
Now it is confirmed it is on porcelain, not enamel, I regret it tends to remove it further from my personal knowledge.
Although I have a lot of miniature portraits, there is only one on porcelain in the collection that pre-dates 1850 and that lone one is British from around 1820 and comes from the Derby factory. There are a number of other porcelain ones in the collection, which are nearly all German, but they mainly date from around 1880-1915.
As I say it is really outside my field, but possibly to progress further, I think you could look up porcelain reference books, especially German ones from the mid 18C to mid 19C. That is, rather than you looking at more miniatures, I would suggest you instead research the porcelain technique.
I think porcelain experts are much more likely to help you with the age and origin, rather than art experts. The porcelain looks more like hard paste than soft paste to me. British porcelain tends to be soft paste, whereas Continental is usually hard paste. Thus knowing whether it is soft paste or hard paste would help decide the origin.
I have a feeling I might have seen similar German portraits on the sides of porcelain tankards, vases, or on plates. I have a feeling that British porcelain was in its infancy around 1750, so that plus the hard paste, is why I lean towards German, as they developed higher skills at an earlier date than the British factories. (I am presuming it has a smooth edge, and so has not been cut down from a porcelain tankard.)
You could also follow up with FREDERICK GLAUSER, who is the author of eBay Guides - COLLECTING EUROPEAN PORCELAIN PORTRAITS THEIR VALUE
Thus any comments which might help more closely determine the age, origin, or identification of the sitter would be very welcome.