Greenhouse with old windows

[sunnycusack]

Hi there,
Hoping someone can offer their advice. I am planning on reusing approx. 30 yr old windows to make a small lean-to greenhouse. The layer between the wooden frames and glass is crumbling and I am not entirely sure whether this is the old putty. The frames have been stripped of paint/stain, and want to get started on preparing the windows for new use. I am sure that in the past my parents have led me to believe the windows are old double glazing, and have read that certain window putty cannot be used for double glazing (however I'm sure this refers to modern double glazing units). I have attached a couple of photos in case that helps. Any help is appreciated!

 

[crank39]

Its putty and in all likelihood will be linseed based putty which does not go down too well with DGUs, how they'e lasted 30 years is a miracle, lucky to get 30 months if bedded on linseed, more modern way now is to use glazing silicone, that said don't bother trying to remove the DGU from the frame now, the putty has moulded itself around the contours around the edge of the DGU and they're virtually impossible to remove in one piece, better to carefully scrape out all the loose putty and reapply new stuff, probably go for butyl putty