Many miniature portraits are unsigned. Sometimes it is easy to pick the artist by their style. In other cases it is difficult and different people can have different opinions.
This miniature was purchased at the Dennis Auction sale in September 2009 and is a good example of varying opinions.
It had a label on the reverse, attributing it to E Tisdale (1771-?). However, I did not believe it was by Elkanah Tisdale, as it was unlike other examples of his work, including one attributed to him in this collection, see Tisdale, Elkanah - portrait of a man
From comparing the miniature with examples in the biography of Edward Green Malbone by Ruel Tolman, I was of the opinion it might be by Malbone. There are about a dozen similar examples illustrated there, some of which are shown below. They were painted between 1801 and 1803, and I would date this example to the same period.
Hence, I decided it was worth the bidding risk. In the event the opinion of a kind expert is that the portrait is may not be by Malbone.
Comparison of the eyes, background and modeling will show that they are by different hands. Look especially at the placement of the eyes. Malbone just doesn't place them at an angle as in your lady. Look at this pic as well as the pics on your blog...the eyes are all on a relatively even keel. The exception to this is when Malbone painted the face in partial profile, which he usually did with the head slightly inclined forward. In that case the eyes, of course, have to be on a slight angle. Frankly, your woman looks very English (and as you said, it doesn't look like Tisdale).
However, sooner or later a collector needs to take a personal risk over an attribution. Sometimes that will be correct, as with a recent purchase of two unsigned miniatures by Nathaniel Rogers, on other occasions there may be disappointment, but it is only by handling many miniatures and having a good reference library that one can learn to differentiate artistic styles. 1375
Being initially largely self taught, Malbone did change his style during his short career.
There is one other miniature by him in this collection, where the attribution has been confirmed by a kind expert.
It is a little earlier in date and stylistically less mature, I think it dates from around 1796.
See Malbone, Edward Greene - portrait of a man
The pose is similar and the cheeks have the same bluish tone. 730