As appeared in “Chubb Collectors” Winter 2003
http://www.chubbcollectors.com/Vacnews/index.jsp?form=2&ArticleId=151
Cleaning Stained Glass Art and Windows
December 3, 2003
One of the most often-asked questions I have heard over the years from people who collect stained glass art and windows is how to clean them properly. They feel intimidated and fear damaging the stained glass. Therefore, stained glass art and windows are rarely ever cleaned at all.
Stained glass windows are designed and engineered to be waterproof. The have to stand up to wind and rain throughout the years. A stained glass window is made to be strong, long lasting, repairable, weatherproof and beautiful. That is a big task for an art medium. It is a task the stained glass window has been performing well for more than a thousand years.
The average old leaded stained glass window nearing 100 years old and still installed in the original building has probably been cleaned only a few times. Chances are good it has been cleaned only as high as an average workman can reach from a small stepladder. Larger stained glass windows that extend 16 to 30 feet high might never be cleaned above the 8-foot level.
Most older windows have been repaired several times. They bear the marks and scars of hailstorms, BB guns, thrown rocks, bullet holes and various wind-loading problems. Repairmen have replaced individual pieces of glass, smeared silicone sealant over cracks, glued false-lead flanges over cracks and gobbed putty or tar in small holes for generations. Many older windows have had additional tin-coated steel braces soldered on to hold the weight of the slumping lead channels. Some unlucky installations have had varnish brushed on to the interior by “con-man” restoration personnel. I have seen windows on which workmen have applied silicone sealant to the exterior around every glass to reseal a leaky window. Getting to ground zero by removing prior bad repairs is sometimes difficult and expensive… if at all possible.
During the 1950s and ‘60s, stained glass studios installed thousands of acres of storm glass coverings on the exterior of stained glass windows to protect them from the elements. In the 1970s and ‘80s, they switched to Lexan polycarbonate plastic glazing sheets, which yellowed and hazed badly in a few short years.
For the most part, the storm window coverings did protect the stained glass from damage, but they also trapped moisture and condensation. In addition, they trapped heat that caused damage to the stained glass. Wood frames rotted, iron frames rusted and intricate carved stone frames were soaked with condensation that froze and spalled the stone.
Overall, the condition of the majority of older architectural stained glass, primarily in churches and public buildings, is fair to rather poor. This glass deserves better treatment and appreciation, but maintenance costs are often more than the owners can bear. Moreover, not all repair people are well trained and equipped to use historic conservation techniques. Many repair people will mistakenly recommend complete re-leading instead of well-conceived restoration techniques.
Cleaning older art and windows can be as simple as gently dusting them off. Cleaning is a process of starting with the least intrusive technique and working through a series of steps that involve water, soaps, oil-based solvents, stronger cleaners and abrasive cleansers. You may not need to progress past water and a towel, or you may need to try each step until an effective process is found.
Stained glass art and windows with scenes and figures as well as colored glasses have kiln-fired paintwork applied to the interior glass surfaces. The “paint” I am referring to is ground glass with a high lead content to lower its melting point mixed with metal oxides… similar to glaze on a piece of pottery. It is applied by brush in a series of steps by a glass painter. The glass artist intended the paintwork to be permanently fused and fired onto the glasses at temperatures around 1,000 degrees Fahrenheit, but exact temperature monitoring was not entirely practical in old-time studio kilns. Some paintwork is overfired, some is well-fired and some is underfired. Underfired paintwork is unstable and can be easily removed even with gentle dusting of the surface. An unknowing person could inadvertently erase special shading and line from the glasses. Some well-meaning people have “cleaned” windows so well that they removed what they thought was “dirt”… and subsequently ruined the windows by removing the paintwork.
You need to test each piece of painted glass prior to cleaning to determine if the surface paintwork is fused well or loose. If it is fused well, you can continue. If it is loose, you must stop.
Some finer art and windows have multiple layers of glasses “plated” together. Dirt can accumulate under the layers. The only real way to clean between plated glass is to remove the layers, clean between the layers, and then resolder the layers–a job for well-trained experts only.
Typically, water can be used for most simple cleaning inside and outside. Towels should be placed on the windowsill to catch the dirty water. Starting at the top of the window and working down, wet the window and simply wipe gently with a sponge. Dry with paper towels.
Stubborn dirt deposits can be cleaned with soap and water. Automatic dishwasher soap is strong and should only be used after trying milder soap first. You might work up to stronger soap solutions if needed. The rule is to start light and work up if needed. One set of windows in a church in Oak Park, Illinois, which I cleaned in 1985, was so dirty and so encrusted that I worked up to toilet bowl cleaner before the dirt loosened–not recommended as a starting point and dangerous to handle. Do not do this at home!
You might be amazed at the beauty of your art and windows if they are cleaned. Do it yourself and save or hire a stained glass studio. Washing inside requires drop cloths, and you may need to repaint afterwards. Washing outside is best accomplished after removing the storm coverings from the windows and using sturdy scaffolding.
You likely will need to reputty and paint wood frames after cleaning to complete the project.
Studios carry insurance for liability if damage is caused. Historically important art and windows must be photographed prior to cleaning to record the process. There are numerous books and articles on conservation techniques for historic building elements that you can follow.
James Jensen is an agent with Church Mutual Insurance Company, the nation’s leading insurer of church properties. Mr. Jensen joined Church Mutual Insurance Company in 1997 after more than 25 years working in stained glass as an artist, preservation specialist and studio representative for firms such as Willet Stained Glass Studio in Philadelphia, Hauser Art Glass Company in Minnesota, Shenandoah Studio in Virginia and Gaytee Stained Glass Studio in Minnesota. Mr. Jensen received a master’s degree from the University of Wisconsin-Madison in hot glass and art history while studying with Harvey K. Littleton in 1977. Mr. Jensen works with the loss control department of Church Mutual to help train other agents on valuation of stained glass and other ecclesiastical art located in churches throughout the country.