Mark and period Qing bronzes are rare. Most 'later' bronzes have apocryphal Xuande seal marks or regular six-character marks and can only be dated between the 16th and 18th Century with more or less certainty on comparative and stylistic grounds.
Compare the enamel handwarmer illustrated in Tributes from Guangdong to the Qing Court, p. 86, pl. 47 and the cloisonne version illustrated in Great National Treasures of China, col. pl. 49.
Tsang and Moss illustrate a bronze warmer by Hu Wenming in Arts from the Scholar's Studio, p. 253, no. 246 and note, rightly enough, that 'For the scholar in need of digital flexibility for painting and writing, the hand warmer was an essential piece of winter paraphernalia'.