Historic Glass Preservation & Restoration Guide for DMV Homes

Original glass in a historic home is more than a window — it is a tangible connection to the past. The imperfections, waviness, and subtle color variations in antique glass tell the story of historical manufacturing processes that no longer exist. Once original glass is removed or broken, it can never be truly replicated. Preserving historic glass maintains the authenticity, character, and often the monetary value of your DMV historic property.

The Washington DC metropolitan area contains an extraordinary concentration of historic properties. Georgetown row houses dating to the late 1700s, Capitol Hill townhomes from the 1800s, Old Town Alexandria colonials, historic Annapolis waterfront homes, and Victorian-era houses throughout Arlington and Silver Spring all may contain original glass worth preserving.

Virginia Glass Windows specializes in historic glass — maintaining, repairing, and when absolutely necessary, replacing it while respecting architectural heritage and meeting preservation board requirements.

Crown glass, manufactured from the 1600s through the mid-1800s, was made by spinning a blown glass bubble into a flat disc. It produces a distinctive bullseye pattern at the center and subtle concentric ripples across the surface. Crown glass is extremely rare and valuable in DMV properties — finding it intact in a Georgetown or Annapolis home is a significant historical discovery.

Cylinder glass (also called broad sheet glass) became the standard from the mid-1800s through the early 1900s. Made by blowing glass into a cylinder, cutting it open, and flattening it, cylinder glass has characteristic slight waviness and elongated bubbles running in one direction. This is the most common historic glass found in DMV homes from the Victorian and Federal periods.

Early machine-drawn glass from the early to mid-1900s shows more uniformity than hand-blown types but still exhibits subtle distortions and seed bubbles absent in modern float glass. Homes in Chevy Chase, Kensington, Takoma Park, and similar early suburban DMV communities often feature this transitional glass. Plate glass, ground and polished to near-optical clarity, was used in high-end DMV properties and commercial buildings from the late 1800s onward.

Washington DC Historic Preservation Office (HPO) reviews exterior alterations to properties within designated historic districts and individually landmarked buildings. Glass replacement on the exterior of a DC historic property typically requires a permit and HPO review. The standard is to preserve original glass whenever possible and use period-appropriate replacements when preservation is not feasible.

For properties in DC historic districts like Georgetown, Capitol Hill, Dupont Circle, Logan Circle, Kalorama, and Woodley Park, any window work visible from the public right-of-way requires HPO review through the Historic Preservation Review Board (HPRB) or staff-level review for routine repairs. Virginia Glass Windows has experience navigating this process and can advise on what requires review versus what qualifies as routine maintenance.

The key to smooth HPO approval is demonstrating that the proposed glass work preserves as much original material as possible. Repairing original glass in place, carefully reglazing with historically appropriate putty, and using restoration glass for replacements are approaches that consistently receive HPO approval. Virginia Glass Windows prepares documentation and photographs to support permit applications.

Virginia Department of Historic Resources (DHR) and the Virginia Board of Historic Resources oversee historic properties in Virginia. Properties listed on the Virginia Landmarks Register or the National Register of Historic Places have preservation guidelines that affect glass replacement. Arlington, Alexandria, Fairfax, and Loudoun County each have their own Architectural Review Boards (ARBs) or Historic District Review Committees that review exterior changes.

Old Town Alexandria is particularly strict — the Board of Architectural Review (BAR) reviews all exterior alterations in the historic district, including window glass changes. The BAR expects original glass preservation and period-appropriate replacements. Similarly, the City of Falls Church and the Town of Leesburg have active historic preservation programs affecting glass work on designated properties.

In Maryland, the Maryland Historical Trust (MHT) administers the state historic preservation program. Montgomery County Historic Preservation Commission, Prince George County Historic Preservation Commission, and Frederick City Historic Preservation Commission all review exterior work on designated properties. Virginia Glass Windows works with property owners to understand which preservation body has jurisdiction and what approvals are needed before beginning work.

When historic glass must be replaced due to breakage or irreparable damage, period-appropriate restoration glass is available from specialty manufacturers. Restoration glass is intentionally manufactured with subtle imperfections — slight waviness, seed bubbles, and surface variations — that mimic the characteristics of antique glass. It is produced in grades from light distortion to heavy distortion to match different historical periods.

For homes from the late 1700s and early 1800s, heavy restoration glass with pronounced waviness and bubbles most closely matches the original crown or cylinder glass. For late 1800s and early 1900s homes, light restoration glass with subtle imperfections matches the machine-drawn glass of that era. Virginia Glass Windows maintains samples of restoration glass in multiple grades for comparison with your original glass.

Restoration glass costs significantly more than modern float glass but is a fraction of the cost of genuine antique salvage glass. For properties under preservation review, restoration glass is typically the required minimum standard for replacement. Virginia Glass Windows sources restoration glass from established manufacturers and can provide samples and specifications for preservation board submissions.

Reglazing is the most common repair for historic windows. Original glass is carefully removed from the sash, the old putty and glazing points are cleaned away, and the glass is reset with new historically appropriate glazing compound. This process preserves the original glass while restoring the weathertight seal. Virginia Glass Windows uses linseed oil-based glazing putty that matches the historical appearance.

For cracked but intact historic glass, stabilization techniques can extend the life of the original pane. Clear archival adhesive applied along the crack prevents further propagation while maintaining the visual appearance. This approach is often preferred by preservation boards over replacement, as it keeps the original glass in service.

When a historic sash requires structural repair, Virginia Glass Windows carefully removes the glass, repairs or reproduces the wood sash components, and reinstalls the original glass. Our technicians are trained in traditional glazing techniques and understand the expansion and contraction characteristics of antique glass that differ from modern float glass. Contact us for a free assessment of your historic windows.