Tool for burnishing copper foil on stained glass pieces.
Today's lathekins are designed to be multi-purpose. Most designs can also used to open lead came and clean putty.
For stained glass artists, the terms lathekin, fid and burnisher are frequently used interchangeably.
Note to readers: I searched unsuccessfully for the etymology of the word lathekin. If someone can tell me where this word comes from I'll update this entry and credit the person who provides the info :-)