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Hours of dedication, bundles of cotton swabs and plenty of patience will be needed to return Taranaki Cathedral’s stained glass windows to their former splendour.

As part of the Taranaki Cathedral remediation and development project, the church’s array of stained glass windows, many of which have deteriorated over time, will be restored, bringing out the details and colours the artists intended.

“As far as we are aware, they have had minimal maintenance over the years and a number are failing,” Cathedral Project remediation and development manager Jenny Goddard says of the windows, some of which date from the 1860s.

“With the building undergoing a lot of work for earthquake-strengthening, it gives us the opportunity to get on and fix them.”

Leading the glass work is Graham Stewart (right), of Stewart Stained Glass Ltd, based in Rangiora, north of Christchurch.

Graham has close to 50 years’ experience conserving, restoring, designing and producing stained glass windows for private and public spaces. Since the Canterbury earthquakes, the family business has been heavily involved in the removal and restoration of stained glass windows from many of the region’s iconic buildings, including Christ Church Cathedral and the Canterbury Provincial Chambers.

Graham was recently in New Plymouth to meticulously measure and document the condition of each window, and determine a plan for removal and restoration.

He says for a number of the windows, the lead structure supporting the stained glass has collapsed through a combination of moisture and the installation methods used.

“A lot of the sealant has gone, which has caused moisture to get in and deteriorate the glass and paint, meaning a lot of the detail in the pictures has been lost. There is also glass damage to many of the windows and some glass lost altogether.

“On many of the windows not enough horizontal steel bars have been used to support the glass. They have tried not to disrupt the picture by spacing the bars further apart, but there is too much space between each one,” Graham says.

“Overall, the windows have held up well considering they have been exposed to the sun and rain for a long time, but everything has a finite life.”

While a detailed plan is yet to be determined, it is likely some windows will be restored on-site, and a number will be removed and transported to Graham’s studio for the long, slow restoration process.

It is a delicate job, with up to four people needed to remove the windows by cutting them away from the concrete mortar. They will then be carefully placed in protective boxes for transportation.

Over a period of months, the lead and glass will be slowly chemically treated and the sealant broken down, so that the windows can be dismantled and taken back to their original state.

“Every piece has to be physically cleaned with cotton swabs, which is very time-consuming and takes a lot of patience,” Graham says.

“Then we assess each piece and determine whether it also needs remediation.”

The windows are then reassembled for installation.

To protect the windows from moisture, as well as vandalism and bird strike, a protective, toughened layer of glass will be installed on the external side of the windows, doing away with the wire mesh which detracts from the visual impact of the stained glass.

A layer of sound proof glass may be also be installed on the external side of the windows in the chapel and the stained glass shifted into the internal side of the frame.

“Once restored and installed, with the methods used today, the windows can last for at least another 200-plus years if well maintained,” Graham says.