On the base of these bowls - half covered by an export aproval "Jian Ding" seal, from Beijing Cultural Relics Bureau - is a red rubber stamped enamel mark of the "Jiangxi Min Ci".
The bowls are therefore likely to have been made in 1940 to 1960.
I got these nice pictures from Simon Ng in Hong Kong and found them well worth publicing as a reference for 20th century enamels - and the "Jian Ding" seal.
Many believe that this seal is a guarantee that the piece is antique, when it is the opposite.
The "Jian Ding" seal is a guarantee issued by the Cultural Relics Bureau in Beijing, that the item is NOT antique, and therefore allowed to be exported.
The age limit on the items was previously "not older then 100 years" but seems today in practice have been extented to "not older then 150 years".
For more information on this kind of marks, seals and pieces, kindly visit the MARKS section on this site.