Most of this glass appears in homes from 1870 to the 1930's. You can still see the wavy nature of this glass as there still striations as the glass was lifted. After industrialization, the process and methods for making glass didn't change. However now machines made the process more efficient.
Wavy glass is the "cool-looking" glass commonly found in older window panes, doors, and furniture built prior to the early 1900s. Generally, the further back in history you go, the wavier the glass is. As craftsmen improved their methods over time, the wave and distortion became less apparent.
Properties of Wavy Glass
Glass produced between the 1700s and early 1900s have this antique “wavy glass” appearance. Another name for the old-looking glass is restoration window glass. The distortion and imperfections appear when looking at the glass from angles or looking straight through it.
You'll most often find wavy windows in homes built before the 20th century, although glass doesn't get wavy overnight. Slowly, the glass in homes built in the early part of the 20th century will also begin to feature this unique distortion. It's somewhat of a myth that wavy windows are due to sheer age.
While some people believe that the waviness is the result of the glass warping over time, the real reason for the wavy appearance has to do with the way glass was made at the time the home was built. There are two types of glass that were used in the 19th century: crown glass and cylinder glass.
For between $5 and $50, you can often walk away with some old glass. how much you'll spend just depends on the size and waviness of the glass. AGW makes some great wavy glass in several different grades of waviness to help you match the glass to the age of your project.
Contrary to the urban legend that glass is a slow-moving liquid, it's actually a highly resilient elastic solid, which means that it is completely stable. So those ripples, warps, and bull's eye indentations you see in really old pieces of glass “were created when the glass was created,” Cima says.
According to AntiqueBottles.com, bubbles are rare in glass produced after 1920, so the presence of a bubble may help to date a bottle or window.
1700s, early 1800s
Plate glass was introduced c. 1700 but would not become the dominant process over crown glass until the 19th century. Crown glass involved a blown glass bubble flattened, reheated then rotated to create a dome shape. It could then be cut into shapes or filled in as appropriate.
Sash Windows
Each of these type of antique windows usually has wood sashes, also known as muntins or lites, that framed the window and held the individual panes.
How Glass Was Made in the 1800s. By the late 1800s, glass was being made by blowing a very large cylinder and allowing it to cool before it was cut with a diamond. After being reheated in a special oven, it was flattened and affixed to piece of polished glass which preserved its surface.
During the early 17th century, window glass was first manufactured in Brittain. It was during this time that glass windows started to become more popular for homes across the western world. The manufacturing process was still crude.
The 9th century BCE produced the first instance of colorless glass. The first manual on glassmaking dates to 650 BCE and was written on Cuneiform tablets (likely called “Glass from the Past,” though this has yet to be confirmed by archaeologists).
Glass panes on windows and doors were also considered a luxury during the 1600s. Only the exceedingly wealthy had them and they set people back so much that they only installed windows in important rooms. Glass was an aristocratic feature and was so rare that people even took down the windows when they weren't in use.
It also was in the early 17th century that English settlers brought glass-making to America, where the first glass factory was opened in Jamestown, Virginia.
Windows were equipped with wooden shutters secured by an iron bar, but in the 11th and 12th centuries were rarely glazed. By the 13th century a king or great baron might have "white (greenish) glass" in some of his windows, and by the 14th century glazed windows were common.
Search for records of previous repairs to the windows or frames. If you can identify the studio or craftsperson who did the work, you may be able to find further records through them, which may identify the age of the windows.
Ancient Rome was the first civilization to have glass windows. It discovered the technology of mixing sand and other component materials and heating the mixture so it could be pressed and cast into small pieces that were formed into panes.
The Kosta factory in Sweden also produced bubble glass designs in the 1950's and the two shown above on the left are from Japan. In the 1950's Blenko Glass made a series of small bowls and ashtrays with patterns of bubbles in rows.
If you examine a piece of pressed glass you will always find either two, three or four seams running through the glass, although sometimes the seams were well hidden in the pattern.
While not all old bottles are valuable, an older bottle is more likely to be worth more than a newer one. Seams and pontil marks are two of the ways you can determine a bottle's age. The pontil mark is the mark at the bottom of the bottle where it was attached to the glass blower's pontil rod.
Just like a human body, windows will age over the years and can't do certain things they could back in the day. The bottom line is, windows age. When they age, they become weaker and break. Windows have to face intense elements day in and day out, so it's clear why glass thins and frames crack.
To create the wavy glass look, squeeze out a little of the window coloring and spread around with a spoon to create that wavy texture. Though it's white while wet, it dries clear!
Soda-lime glass production involves mixing together silica with 'soda' or sodium carbonate, and 'lime', or calcium oxide, before heating them together in a furnace at temperatures of around 1320 degrees Celsius. The molten mixture produced as a result is then worked into a shape and left to cool, producing solid glass.
Cylinder glass is one type of antique, mouth-blown window glass found in historical buildings dating back to the 1600s. It's also known as wavy glass for the bubbling, undulating imperfections found in the surface of the glass that distort images when you look through it.