More than £850,000 has been spent on galleries at Norwich Castle - because of fears museums were on the brink of refusing to lend items for major exhibitions.
Yet visitors to the Norwich Union and Bernard Matthews exhibition galleries are unlikely to notice much visual difference after the six-month project.
But for museum bosses, the work has solved a long-standing problem over how to control the humidity in the galleries.
The rooms were originally designed as a prison wing, not to be a gallery where precious objects go on show.
And the battle to keep humidity at a constant level meant the museum was in danger of missing out on loans for its popular temporary exhibitions.
Before lending items, museums require evidence they will be displayed in an environment where the temperature and humidity does not fluctuate - and the museum was unable to provide that assurance.
So the £855,000 Project Refresh saw improvements made to the environmental management systems for the galleries.
A new air handling plant has been installed to better maintain the humidity levels in the galleries, while insulation has been improved and specialist wall linings replaced.
Stuart Garner, Norwich Museums operations manager, said: "This is the most important exhibition space in the county and the loans come from all over the place.
"But it had become more and more of an issue as to whether we were looking after the paintings and artefacts.
"We needed to be able to provide evidence, for months before loans were made, that there was a stable climate in the galleries.
"The problem was that, with two galleries, the old system was struggling to handle it.
"It was really important that we did this work in order to be able to host major exhibitions. And we hit budget and timescale."
The galleries will, next year, be displaying the finds from the 17th century royal shipwreck the Gloucester, found off the coast of Great Yarmouth.
The temporary exhibition 'The Last Voyage of the Gloucester: Norfolk’s Royal Shipwreck’ will go on show at the castle, which is in the midst of the £15m Royal Palace Reborn revamp, from February to July next year.
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