Installing Glass in Clock Doors: Putty, Points, or Pins

This article focuses on choosing appropriate methods for installing glass in clock doors including traditional putty made from plaster of Paris and burnt umber, linseed oil glazier's putty, small pins for longcase and bracket clocks, and modern glazier points. We'll cover why putty adds structural integrity, making authentic-looking putty, removing hardened putty safely, and when alternative fastening methods are appropriate.

Understanding traditional putty methods

Why clock makers used putty

Putty serves multiple purposes beyond just holding glass in place. It adds structural integrity to the door by binding glass firmly to the wood frame. The putty creates a weather seal that keeps dust and moisture out while supporting the glass against vibration and handling. Traditional putty also creates the authentic appearance appropriate for antique clock restoration.

Two types of traditional putty

Clock makers used two different putty formulations depending on location, time period, and personal preference. One type combined plaster of Paris with burnt umber powdered dye to create a dark, firm putty that matched wood tones. The other used white linseed oil putty common for window glazing. Both work well initially, but each presents different challenges for future repair or glass replacement.

Making plaster of Paris putty

Mixing plaster and burnt umber

Mix plaster of Paris with burnt umber powdered dye to create dark putty that blends with wood tones. The burnt umber provides color that looks more authentic than white putty against stained wood frames. Mix the dry powders thoroughly before adding water to ensure even color distribution. Add water gradually while mixing to achieve proper consistency—you want stiff putty that holds shape but remains workable.

Sourcing burnt umber powder

Powdered burnt umber is readily available from artist supply stores—it's a commonly used pigment available as powder or paint. You can also order from woodworking suppliers who carry dyes and pigments. Buy enough to mix several batches since you'll want consistent color across all putty applications on a single clock.

Working time and curing

Plaster of Paris putty sets relatively quickly, so mix only what you can use in one session. Once mixed, you have perhaps 30-45 minutes of working time before it becomes too stiff to apply properly. The putty continues curing for several days, gradually hardening to rock-solid consistency. This hardness provides excellent support but makes future removal challenging.

Using linseed oil putty

Advantages of oil-based putty

White linseed oil glazier's putty is traditional window glazing material. It remains somewhat pliable longer than plaster putty, giving you more working time during installation. Oil putty seals well and holds glass securely. It's readily available at hardware stores, unlike specialized plaster/umber mixtures you must make yourself.

The removal problem

Over decades, linseed oil putty cures to rock-hard consistency that's nearly impossible to remove without damaging glass or wood. When oil putty must be removed for glass replacement, expect extremely difficult work with high risk of breaking the glass. Many restorers consider hardened oil putty the worst substance to deal with in clock repair—removal requires patient scraping, picking, and considerable prayer.

When oil putty makes sense

Despite removal difficulties, oil putty remains appropriate for restoration when authenticity matters and the glass won't need replacement. If you're installing reproduction glass in a door that originally had oil putty, using the same material maintains historical accuracy. Just understand that future repairs will be challenging.

Alternative fastening methods

Small pins for longcase and bracket clocks

Cabinet makers traditionally used small pins (tiny nails or brads) to secure glass in longcase and bracket clock doors. This method allows glass removal and replacement without the permanence of putty. The pins are nearly invisible when properly installed and provide adequate support for protected indoor clock doors. This approach respects tradition while facilitating future maintenance.

Modern glazier points

Metal glazier points provide secure glass installation without putty's permanence. These small triangular or push-type fasteners hold glass firmly while allowing easy removal for future repairs. Many restorers use glazier points for their reversibility—if future owners need to replace glass, points release easily without damage to wood or glass. However, points don't add the structural reinforcement that putty provides.

Rope or cord decorative edge

Some restorers consider using decorative rope or cord to cover glass edges and hold glass in place. While this might seem like an attractive solution, most experienced clock restorers strongly dislike this approach. It looks inappropriate and inauthentic on antique clocks. Rope draws attention to itself rather than letting the clock case and glass blend naturally. Stick with traditional putty or discreet fasteners that maintain period-appropriate appearance.

Removing old putty safely

Assessing putty hardness

Before attempting removal, test the putty's hardness in an inconspicuous area. Softer plaster-based putty sometimes yields to careful scraping and picking. Rock-hard linseed oil putty requires more aggressive techniques with higher risk of damage. Understanding what you're dealing with helps you plan the removal approach and manage expectations about glass survival.

Scraping and picking technique

Use thin, sharp tools like artist's palette knives, dental picks, or small chisels to gradually work putty away from glass and wood. Work slowly and carefully, removing small amounts at a time. Never force tools between glass and wood or you'll crack the glass. Accept that this is tedious, time-consuming work—rushing causes damage. Judicious scraping, patient picking, and considerable prayer constitute the standard approach.

Accepting glass loss

When putty is extremely hard and glass must be removed, glass breakage is likely. If the glass is original and has value, removal becomes a calculated risk. Sometimes the best approach is leaving puttied glass in place unless absolutely necessary to remove it. If glass is already damaged or needs replacement anyway, putty removal becomes less stressful since glass breakage doesn't matter.

Applying putty properly

Preparing the rabbet

Clean the wood rabbet (the recessed groove that holds glass) thoroughly before applying putty. Remove all old putty, dirt, and loose wood fibers. A clean surface ensures good adhesion and proper sealing. Dry the rabbet completely—moisture interferes with putty curing and adhesion.

Installing glass with putty

Apply a thin layer of putty in the rabbet, press the glass into place, then apply putty around all edges, pressing firmly to ensure contact with both glass and wood. Tool the putty smooth with a putty knife or your finger, creating neat beveled edges. Remove excess putty from glass surface immediately—dried putty on glass is difficult to clean off.

Minimal practice required

Putty application requires only minimal practice to achieve good results. Work on scrap wood or an old door first if you're uncertain. The material is forgiving—you can smooth and reshape it until you achieve the appearance you want. Taking time to do it neatly pays off in professional-looking results that enhance rather than detract from the clock's appearance.

Considerations for valuable clocks

Matching original installation method

For museum-quality or particularly valuable clocks, match the original glass installation method. If the clock originally had plaster putty, use plaster putty. If it had pins, use pins. This preserves authenticity and maintains value. Modern methods like glazier points, while practical, may not be appropriate for the most important pieces.

Documenting before removal

Before removing old putty or glass, photograph the installation thoroughly. Document putty color, application style, and any maker's marks or labels the door might have. This documentation guides authentic restoration and provides historical record if something goes wrong during the work.

FAQs

Why did clock makers use putty instead of modern fasteners?

Putty adds structural integrity to the door beyond just holding glass. It creates weather seals, supports glass against vibration, and provides authentic period-appropriate appearance. Putty also doesn't loosen over time like some mechanical fasteners might.

What's the difference between plaster of Paris putty and linseed oil putty?

Plaster of Paris mixed with burnt umber creates dark, fast-setting putty that matches wood tones. Linseed oil putty (white glazier's putty) stays workable longer but cures extremely hard over decades, making removal nearly impossible without damaging glass.

How do I make traditional plaster of Paris putty?

Mix plaster of Paris with burnt umber powdered dye (available at art supply stores), then add water gradually to achieve stiff but workable consistency. Mix only what you can use in 30-45 minutes—it sets quickly.

Can I use modern glazier points instead of putty?

Yes, glazier points hold glass securely and allow easy future removal. However, they don't provide the structural reinforcement and weather sealing that putty does. For valuable antique restoration, match the original installation method for authenticity.

What's the best way to remove hardened putty?

Use thin, sharp tools like palette knives, dental picks, or small chisels. Work slowly, removing small amounts at a time. Never force tools between glass and wood or you'll crack the glass. Accept that this is tedious work—patience prevents damage.

Should I use decorative rope to hold glass in clock doors?

No, most experienced restorers strongly dislike rope or cord approaches. They look inauthentic and draw attention rather than blending naturally. Use traditional putty or discreet fasteners for period-appropriate appearance.

Is it likely to break glass when removing old putty?

Yes, especially with rock-hard linseed oil putty. If glass is original and valuable, removal becomes a calculated risk. Sometimes the best approach is leaving puttied glass in place unless removal is absolutely necessary.