While there are some reputable sellers on ebay selling antique stained glass windows, a great majority of the listings in the antique stained glass window category are actually reproductions which were mass produced using antique looking patterns. Just because someone puts the words Tiffany, Victorian, Arts and Crafts, Mission, Art Nouveau, etc. in their title, it doesn't mean that they are actually antique windows. These are usually reproductions which use the copper foil technique, as opposed to the leaded technique found in true antique windows. The leadlines of old windows do not deviate in width, but remain parallel, while the lines of a newer copper foiled window will get narrower in places and wider in other places, in other words the line width will be more organic looking. (The only exceptions to this are the true Louis Comfort Tiffany or John La Farge windows, which sell for many thousands of dollars, and use the copper foil technique in conjunction with leading.) When you closely inspect the leadlines' joints, you should see the solder joint, not a continuous black line. Exceptions to this are if the panel was encrusted with many years of soot. But then there will be evidence of soot elsewhere as well. Antique windows generally do not have a cute metal hanger on the top of the frame, nor do they have an angled picture frame around them. They generally come in their original sashes, unless the original sash was too deteriorated to save, and these sashes are generally thick - more than an inch thick. Usually you'll also see about a half inch dark line around the edge of the sash where the sash was hidden under the molding and the bare wood is revealed, unless the sash has been repainted after it was removed from the house or the frame was refinished.
Although antique windows are sometimes sold in their original untouched condition, you will usually find that the window has been subjected to some type of repairs in it's long life. Types of repairs may include replaced pieces of glass, solder joint repairs, flattening the panel if it was bowed, calf joint repairs, which are leadlines soldered over the crack on both sides of the glass, and regrouting or recementing the panel, as well as cleaning the panel. If there are repairs, it is the sellers responsibility to inform you of that in the listing, especially if they are obvious repairs. These aforementioned repairs are professional types of repairs, and there are also non professional types of repairs, such as gooping liquid nails or tar over cracks or sagging leads. Those types of repairs are just an abomination because they make embarking on a true repair that much more difficult as they need to be undone first. Depending on the skill and dexterity of the artisan who repaired the window, the lead may have some degree of deformation if a piece of glass has been replaced. This can range from a subtle change in texture or patina (color) to wildly distorted leads which barely hold the glass in place. (Many churches apparently used their handyman's rudimentary skills to fix their old windows.) So, there should be some notation made about the quality of workmanship on repairs in a description. If you buy a window based on one or two tiny pictures and a scant description, don't be surprised if what you get is not what you expected. If you buy a window and start to clean it, don't clean under the leads, as this is the grout or cement, which belongs there. It waterproofs and rigidifies the panel. Most old windows have some degree of grout loss, as old grout tends to dry out, and crumble.
Many old windows also have iron, steel, or zinc reinforcement bars, which run horizontally or vertically across the panel, and are either soldered directly to the leading, or are attached by means of wires twisted around them, which are soldered to the panel. Don't remove the support bars, especially with a larger window ! They are the masts of your ship, so to speak, and without them your panel is more vulnerable to bowing and sagging. The majority of bowed windows are not intentionally bowed. This bowing is usually caused by the wood frame becoming wet after paint loss, and expanding, thus forcing the window out of plane. This is especially true with concentric designs, be they circles or squares. Bowing can be corrected if the window is removed from the frame and soaked in chemicals, such as diluted TSP, or in some cases, gently manually flattened.
Lastly, opalescent glass was only used in stained glass beginning in the 1880's; the patent for opalescent glass was applied for in 1880 by La Farge. Opalescent glass has a translucent white mixed into the colors. Windows before this time had only clear or transparent colors, usually with a slight texture. Keep this in mind next time you see an opalescent window listed as an 1870's window. Windows from the 1880's generally had transparent colors, or very translucent opalescent colors, and windows prior to that were mostly derivative of English church windows and had enamel painted central medallions and/or backgrounds, or sandblasted/etched designs within a piece of flashed glass. I hope this guide will be of use for your future buying considerations.
For a more detailed discussion on the dating and preservation of antique stained glass windows, please see the link on my "about me" page.
Guide created: 22/09/06 (updated 22/01/14)