Perhaps this plate should be described as a "Cabinet" plate, because since 1845 it has hardly been used. It is one of the cleanest flow blue pieces we have ever had. It was made on December 4th, 1845....this information is available on the English Registry mark which is very readable on the back of the plate. The plate is 9 & 1/4 inches in diameter and other than the crazing (a product of age) it is in excellent condition. This pattern was registered by John Ridgway in England in 1845, according to Godden's Encyclopedia of Marks.
Exceptional Ridgway 1845 Flow Blue Peking Pattern Dinner Plate