If you’re familiar with older homes and buildings, you may have come across original windows that have wavy glass panes. Some parts of the pane are thicker than others, they exhibit ripples on the surface, and they bend light slightly, making objects on the other side look a little skewed. These historical windows can add a touch of class to our historic homes and other buildings, but many people new to these wavy glass windows are unsure whether or not they are strong and energy efficient enough to stand the test of time. 

Luckily, most often historic windows can be made to rival the energy efficiency of a new set of windows, and with the quality materials they were originally constructed from, they’ll last a whole lot longer than that new set. In order to fully understand how we make them last for generations to come, we’ll want to look at what makes old glass window panes wavy and how to rehabilitate them so they work like new.

Why Does Old Glass Look Wavy?

A lot of people have gotten the idea into their heads that the waviness of the glass is caused by settling or melting over years of service. Neither of these is correct. Glass is neither a high viscosity liquid that is slowly settling, nor is the sun hot enough to melt your windows.

The reason this glass is wavy comes down to the history of glass windows and the glass making processes popular at the time the structures were built. Artisans of the past didn’t have the same manufacturing technologies we have today. Their methods were more primitive, resulting in imperfections in manufactured goods that we don’t see today. 

Glass produced before the 1940s was generally hand blown, and individual panes were cut from the large glass plates that resulted. Most vintage windows in the US were created using one of two hand blown glass manufacturing methods. They are crown glass and cylinder glass.

Crown Glass

If your old windows are round in shape, or you can see concentric circular patterns rippled across your rectangular panes, they are likely made from crown glass, also known as table glass. Crown glass is easily identifiable by that bullseye pattern created during the manufacturing process. 

When creating crown glass windows, glass blowers blow a bulb or crown, cut open and spin it so that it flattens due to centrifugal force. The process of spinning the bulb into a flat table is what gives crown glass its signature appearance. Once the glass has cooled and hardened, windowmakers polished it and used either the whole table to create round windows or cut individual panes from the disc.

Crown glass is most often found in very old windows, since the process’s popularity began to wane at the start of the 19th century.

Cylinder Glass

Cylinder blown glass panes are the other type of windows common in a great many historic US homes. The method was an incredibly common way to make window panes in the nineteenth and early twentieth centuries. It is another hand blown method, meaning it also contains the imperfections that produce the appearance of wavy glass, just like crown glass does. Unlike crown glass, the ripples are usually straight, rather than rounded. Again, this is due to the process of production.

Cylinder glass begins by blowing the molten glass into an elongated tube, cutting the ends off, and running a slit along one side from top to bottom. The cut tube is then rolled out onto a flat surface, and pounded flat. Once cooled, the panes were ground, polished, and cut.

This process was more efficient than making panes from crown glass, and with the advent of industrialization, machines made it even more so. It remained the most popular method for producing glass until float glass was introduced in the twentieth century.

Modern Glass

By the 1940s, new glassmaking procedures made it possible to produce panes that were nearly perfectly flat, and no longer had the wavy characteristics associated with antique glass. The hot new process floated molten glass on a bed of molten metal, which is where the name float glass comes from. These flat panes were easier and cheaper to produce, meaning the old-world techniques became almost completely obsolete. 

Float glass is still widely used today. It’s uniform thickness and incredibly flat surfaces give it ultimate clarity and makes quality control and automation a whole lot easier. Since most replacement windows on the market are cut from float glass, many remodelers and rehabbers have been looking for ways to keep the historic charm of their old looking glass. Luckily, you can still get wavy glass panes for your projects.

Can I Update My Windows and Keep the Wavy Glass Look?

When we look into antique window glass replacement, many people want an upgraded set of windows while keeping the wavy glass look. While most new windows are made from float glass, it is possible to find wavy glass that delivers all the benefits of new windows while retaining the historic look you’re after. 

Buying new windows with hand blown glass panes can get expensive quickly, so many of us look to other options. The most sustainable option is to refurbish your old windows to keep them looking great, while also making them more energy efficient and acoustically sound.

Refurbishing your Windows

If you’ve got rotting windows but the wavy glass panes are still in good shape, your best option may be to refurbish and retain the windows you’ve already got. You’ll maintain the historic charm and save yourself a good deal of money over installing all new windows. Here’s what you’ll need to know before getting started.

Replace Rotted Wood

The first thing you’ll need to do to make your windows more structurally sound is to replace any parts of the wood frames and muntins (the wood beams that separate the individual glass panes) that are rotten or broken. You don’t need to completely replace the pieces, if only small portions are damaged. You can cut out the bad portions and replace them with new wood. Sand it down and refinish it, and you should be in good shape.

Make Sure Your Seals are Strong

The most important part of making your windows energy efficient is to seal them well. 

Once you’ve repaired or replaced any bad parts of the frame, you’ll want to make sure the places where your wavy glass panes meet the wood frame are well sealed. Air can easily pass through any gaps around your window panes. Sealing them well prevents hot or cold air from passing through and raising your heating and cooling costs. Use a caulk or sealant that will stand up to moisture and extreme temperatures for the best results.

Add a Second Layer of Defense with Window Inserts

If you want to improve your single-paned windows’ energy efficiency and ability to keep sound from passing through, a great way to do so is to add a second window pane. The most cost effective way to add a second layer of glass is to utilize window inserts to reinforce your existing windows.

Window inserts are available in most standard sizes and can be cut to fit if you have custom windows that need a little more shoring up. They are even available fitted with wavy window glass, meaning you don’t have to give an inch when it comes to retaining the handmade feel of your historic windows.

Get Help from Wavy Glass Gurus

In order to get exactly what you want out of your window upgrades, talking to the pros goes a long way. We’ve got years of experience under our belts, and can let you know what you’re getting into before you find yourself in over your head.

Whether you can get by with wavy glass window inserts or you need a whole new set, the pros will make sure you make the right decision from the get go. If you want to know more about how wavy glass replacement windows or inserts can lower your energy costs and maintain the beauty of your historic home, reach out for a consultation today.