Church Window Restoration
"Baptism of Christ," Tiffany Studios, 1916, Restored by Bovard Studio, 2000

Cementing and Cleaning

Glass Painting

Click to enlarge

Rose Buford (at right) has finished cementing and whiting and is now brushing the panel to remove the waste material. On the left side of the photo other department staff are working on windows that have been placed in front of a light easel for final inspection and cleaning.

Glass Painting

Click to enlarge

Roger Haynes, uses a wood pick to remove any cement that has seeped out from under the flanges of the lead came. The pick is run around all edges of the lead came to cut and remove this excess.

The assembled window is now ready to be cemented. This important process will stiffen and strengthen the leaded panels, making them weather tight, and adding an aesthetically pleasing dark "patina" to the lead surface. The cement or putty is packed into the space between the flanges of the lead came and the glass on both sides of the window, then the excess is cleaned off with a compound call "whiting". There is division among stained glass professionals on the best formula for glazing cement; primarily, whether a hardener (such as plaster or Portland cement) should be added to the glazing formula or if an unaltered commercially produced glazing putty is best. We have found that Portland cement is corrosive to the lead came and over time the lime will leach out producing a haze bordering the lead came that is very difficult to remove. Due to these negative effects our studio does not use Portland cement in our glazing cement.

Another traditional formula for glazing cement contains lead oxide as a primary ingredient. Lead oxide in powder form is easily inhaled and since the human body absorbs four times as much lead into the bloodstream by inhalation than from ingestion, lead oxide is no longer used (see 'Safety and Environment' on next page).

The glazing cement formula that we use has calcium carbonate (a.k.a. whiting) as its primary ingredient. You may recognize this compound from some popular anti-acid medicines, as calcium carbonate is well known to relieve acid indigestion.

The glazing cement is pushed under the flanges of the stained glass window using a stiff bristle brush. The excess cement is cleaned off with whiting and another vigorous brushing. This cleans and polishes the stained glass while another ingredient in the glazing cement, lampblack (carbon), darkens the lead came leaving a rich patina that is neutral in the design of the stained glass window.

Once cemented and cleaned, the stained glass window needs to setup for a few days until the cement has hardened. Some of the cement will have seeped out from under the flanges of the lead came and a wood pick is used to run around all edges of the lead came to cut and remove this excess putty. The stained glass window is then placed on a light easel (in front of a window) or onto a light table for final inspection and cleaning.

NOTE:

When a leaded window is to be installed without protective exterior glazing, industry conservation guidelines specify that it must be sealed in a specific way to safeguard against leaks. The window must be built using flat 'H' lead came, then the lead flanges are bent back slightly and the opened space is hand packed with a linseed oil based putty. The lead flanges are then pressed back down onto the glass and the excess putty is picked off. After whiting and cleaning the window must be laid flat to allow the putty to cure for about 2 weeks.