Your friend wikipaedia even has an entry

https://en.wikipedia.org/wiki/Hacking_knife 

- and a glance at a 1950’s copy of Rycrofts 600 page catalogue confirms the
name. - Generally regarded as a glaziers tool used for hacking ou thte dried
putty when replacing a pane of glass.

- wonder how you clean up all the modern gunk used for bedding glass?  We
have/had some windows glazed into ‘rubber’ gaskets - some had shrunk, many had
corners which were no longer entirely watertight.   Contrast with old fashioned
putty which not only does the job, but makes your hands feel and smell nice at
the same time.


Richard Wilson
Yorkshireman Galoot