Predominant character styles in marks of the Qing dynasty:
Reign
Character style of marks
Shunzhi
1644-1661
Kaishu (no imperial marks?)
Kangxi
1662-1722
Kaishu
Yongzheng
1723-1735
Kaishu
Qianlong
1736-1795
Zhuanshu
Jiaqing
1796-1820
Zhuanshu (imperial)
Daoguang
1821-1850
Zhuanshu/Kaishu
Xianfeng
1851-1861
Kaishu
Tongzhi
1862-1874
Kaishu
Guangxu
1875-1908
Kaishu
Xuantong
1909-1911
Kaishu
The style of character used in a mark can be a hint whether a specific item is doubtful in view to authenticity.
For example, if an item has a mark with Kaishu style of characters, and is supposed to be from the Qianlong reign, then something might be fishy. Most marks during the Qianlong reign, whether imperial or from private kilns did use Zhuanshu characters. Zhuanshu characters are an archaic character type used mainly in seals (seal type marks).
Remark regarding Chinese terms: (Use of Kaishu/Kaiti and Zhuanshu/Zhuanti) Example: Kaishu - means Kai style 'writing'; Kaiti means Kai style 'characters' (aka 'font')