Beginning in July this year, the Glasgow School of Art (GSA) engaged in an initiative to restore the windows on the Scott Street façade of the Mackintosh Building that allow light to flood into its library.
Around 900 glass panels were removed from steel frames that had corroded and were in danger of being lost if not treated.
The frames were taken to specialist metalworkers for structural repair, sandblasting and galvanisation, and work was also done on the stonework around the windows.
The conserved frames have now been replaced and re-glazing work is under way.
The project is part of the GSA's ongoing conservation of The Mackintosh Building and it was supported by grants from Historic Scotland and the John Paul Getty Jr Charitable Trust.
The last repairs to the windows were done in 1947.
The final bill for the work at that time came in at £2125, which is roughly £70,000 in today's money.
Seventy years later, the windows had suffered "excessive corroding" and were in danger of being lost if not treated promptly.
A statement from the GSA added: "There was a long-term risk not only of the irrevocable loss of the iconic windows, but, in an echo of 1946, of their falling out onto the street."
There was also the risk of water damage which could affect not only the building structure, but in particular the irreplaceable interior.
The frames were taken to Samuel McGarva & Son in Renfrew for structural repair.
Work on the external stonework around the windows by specialists from Nicolas Boyes Stone Conservation, whose many other conservation projects have included Rosslyn Chapel in Midlothian, St Giles Cathedral in Edinburgh and the Robert Burns Monument in Dumfries.
After five months of work, the conserved frames have now been reinserted into the openings, glass panels added, including a number of replacements of panes that were fractured and cracked, and the library is once again illuminated by natural light.
Meanwhile, the new £50m Reid Building opposite 'the Mac' is still being constructed.
The new building, designed by Steven Holl Architects of New York and JM Architects of Glasgow, is due to officially open in April.
Holl's design uses three large "driven voids of light" as a key feature.