A hacking knife’s primary function is the removal of old putty from window frames, in order to replace the glass within them.
When the putty holding the glass in old window frames starts to crack and look unsightly it can be very hard and difficult to remove.
Hacking knives have been specifically designed to make this job as easy as possible and minimise damage to the glass panes or frames of the window. The sturdy blades of these tools have other uses as well (see What are some other uses for hacking knives?).
