Glass - Back to the Future!

Presenting Author:
Hans Reiner Meindl
<[email protected]>

article posted 18 Jan 2016

Hans Reiner Meindl

2009 - today Owner and President of Glashütte Lamberts Waldsassen GmbH, Germany

1999 - 2009 CFO of HEINZ Glas and HEINZ Holding, Kleintettau, Germany

1998 - 1999 CEO of Mconsult, Ochsenfurt, Germany

1983 - 1998 Südzucker AG Mannheim, CFO of Südzucker International, Ochsenfurt,

1977 - 1983 University of Regensburg, Germany, MBA

Married, 3 adult children

Member of ICOMOS Germany

Member of ICOM

Member of Society of Glass Technology

Mouth blown UV protective window glass ~ Projects, experiences and further developments

Hans Reiner Meindl

Glashütte Lamberts Waldsassen GmbH, Germany

Over the last years the demand for UV protective glass for valuable art objects and historical furnishings has increased. UV rays damage organic material (textiles, wood, paper) but also modern adhesives which are based on organic materials. Until now the only solutions available were based on organic foil material or a coating of nanoparticles. The coating on the glass is not scratch-proof, over time the foils age and loose their effect. On this basis the author, a managing partner of a glass manufacturing company sought for a solution using glass. He developed a glass in which the UV protection is integrated and is not subject to aging. Thus, during the renovation of the Wittenberg town church, as part of the Luther Decade, the apse was to be glazed to protect the valuable Lucas Cranach Altar from UV rays.

The second project was the UV protective glazing for York Minster, UK. 24 meters tall and about the size of a tennis court, the 311-panelled Great East Window is the largest expanse of medieval stained glass in Britain and regarded as one of the great pre-Renaissance treasures of European art. The east window of York Cathedral (GB) was fitted with a protective glazing of restauro®-UV in order to protect the adhesives used during the repairs from UV rays. The manufacturer, Glashütte Lamberts, is a family owned company in that produces mouth blown sheet glass for restoration. The production of UV protective glass (brand name: restauro ® UV) begins with the gradual mixing of the normal glass ingredients e.g. sand, soda, lime plus cadmium sulfite and zinc sulfite in a glass batch facility. The melting process is done in a ceramic pot at temperatures of up to 1420°C. One feature of the process is that, in the classic way, i.e. with the use of a glassmaker's blowpipe, the functional glass (see above) is combined with a normal basic glass. As most colored glasses the restauro®-UV is manufactured as a flashed glass.

This 2 layer portion of glass is firstly formed to a balloon, later to a large cylinder. After cutting the cylinder lengthwise, reheating and flattening the glass, the first step of manufacturing the UV glass is finished. The second and final step is a defined temperature treatment. At a temperature of more than 600 degrees Celsius and over a certain period of time sulfite colloids are built up in the glass. They form the UV barrier. This UV-glass is available in approximately 50 x 60 cm (2 - 3 mm thickness). It can be used for traditional lead glazing as well as double glazing or laminated glass. During production the manufacturer observes the highest quality. Each sheet undergoes an on-site quality control before shipment. In addition samples from each batch are checked for transmission by an independent laboratory. Typical testing equipment is Lambda 12. Test reports can be made available to customers. Tests are cross checked by peer review. Dr. Hubert Drexler, a graduated chemist, with many years of practical experience in the glass and raw materials industry, contributed his well-founded knowledge of process optimization and significantly shaped the development of this UV protective glass by optimizing the mixtures and accompanying the manufacturing process. His scientific education and the know-how gained during many successful research projects at renowned industrial companies proved to be very valuable. His very special knowledge of the transmission spectrums for colored glasses formed the basis for a systematic report on the correlation between the UV protective properties of the functional glasses manufactured and the relevant parameters in the manufacturing process. The testing laboratory, IGR Göttingen, is a neutral and independent company and has modern equipment including SEM-EDX, ICP-OES, FT-IR and UV-VIS. The development and manufacturing process of restauro®-UV was accompanied analytically by the external laboratory. The main task was the chemical analysis of the glasses produced with the ICP-OES and the measurement of the UV protection with the UV-VIS.

Summary restauro® UV:

restauro® UV is a new development in the glass industry. It protects all material, especially organic, from UV radiation up to 400 nm. Protective glazing of York Minster´s East Window was one of the first projects, until today the by far biggest project. All requirements of YGT were fulfilled at highest satisfaction. As Sarah Brown, director of YGT said: "It is reassuring to know that we are now able to offer total environmental protection for all aspects of the conserved window."

Future prospects and new developments With view to the experiences we´ve made talking to restoration project managers and responsible persons for heritage and listed buildings we understood that there is a demand for an additional IR (infrared) protection. At this stage we are just about developing a new mouth blown window glass which combines UV and IR protection. The author will tell you the latest news on that.