The Art of Glazing – Sealing and Setting Historic Window Glass
Glazing a historic window isn’t just a technical task—it’s an art form. Done properly, it creates a watertight seal, protects fragile glass, and preserves the historic character of your sash for decades. Done poorly… well, you’ve probably seen the cracked putty and mildew-streaked panes that come from shortcuts. In this post, we’ll walk you through what glazing is, why it matters, and how it’s done right—whether you’re restoring a 1920s bungalow or a Queen Anne masterpiece.
What Is Glazing, Exactly?
Glazing refers to the process of setting glass into a window sash using a glazing compound (traditionally linseed oil putty) to hold it in place and seal it from the elements. While modern insulated windows use rubber gaskets or metal spacers, historic windows rely on this hand-applied putty to keep everything snug.
In most traditional windows, you’ll find:
Single-pane glass
Wood sash with a rabbeted opening
Metal glazier’s points (to hold the glass in place)
Hand-tooled putty (the magic that keeps it weather-tight)
Why Proper Glazing Matters
Aside from the aesthetic of clean, hand-tooled bevels, correct glazing:
Keeps water out of the joints and frame
Holds the glass securely without stressing it
Preserves thermal performance when paired with storm windows
Prevents rot by shedding water away from the sash
Poor glazing—especially using silicone or caulking—can actually trap water, creating hidden rot and risking glass breakage.
Step-by-Step: How Glazing Is Done
Remove old putty with a glazing tool or steam to avoid cracking glass
Clean and oil the rabbets (groove where glass sits) to condition the wood
Bed the glass in a thin layer of putty for airtight contact
Insert glazier’s points to hold glass in place
Apply the finish glazing compound at a 45-degree bevel
Tool smooth with a putty knife and allow to cure
Paint the putty line to seal and blend with sash
What Kind of Glazing Compound Should You Use?
Linseed oil putty: Traditional and easy to work with. Paintable.
Latex-based glazing: Dries faster but may crack over time.
Epoxy alternatives: Only for extreme situations. Hard to reverse.
At Austin Historical, we prefer linseed putty because it’s breathable, reversible, and blends beautifully with historic finishes. We have our proprietary Austin’s Glazier’s Putty which is our proprietary blend manufactured for us by Sarco Putty. It provides great workability and mildew resistance. You can purchase it at The Craftsman Store.
Common Glazing Mistakes to Avoid
Using caulk instead of putty
Applying too thick of a putty bed
Skipping the paint seal over cured putty
Neglecting to oil raw wood first
Can You Glaze Over Old Putty?
In some cases, yes—but only if the existing putty is solid and tightly bonded. More often than not, it’s best to remove all putty and start fresh for best adhesion and lifespan.
Historic Glass Deserves Respect
When working with original cylinder or crown glass, extra care is required. These wavy, handmade panes can’t be replaced once broken. Always use padded stops, light pressure, and sharp tools to avoid flexing or cracking.
Final Word
Glazing isn’t just sealing glass—it’s preserving your home’s history, one sash at a time. Whether you’re hiring pros or learning to DIY, respect the craft. It’s one of the most rewarding parts of restoration, especially when sunlight hits your freshly glazed pane and you see that old glass shimmer like a time machine.
