Cleaning Historic Glass
- CSI Division:
- Division 3 - Concrete
- Glass & Glazing
- Last Modified:
Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
- This procedure includes guidance on cleaning glass in existing windows. It also includes methods of cleaning historic glass where the glass is dirty, discolored or etched because of time and negligence.
- Dirt accumulations on glass exposed to weather causes surface crazing and alkaline reaction opalescent films if not washed at least every several years.
- Discoloration is an oily film on the surface of the glass. It is caused by oil, coal, and other fossil fuels existing in the atmosphere, by magnesia dioxide photo- oxidizing in the glass under strong ultra-violet light, or by the addition of excessive alkali salts to produce a colorless product.
- Etching is scratching of the glass produced by vigorous cleaning, steel wool, abrasive papers, or kitchen scouring compounds. Etching can occur on windows that have been exposed to wind blown grit, or left unprotected during sandblasting of masonry buildings. Etching can also be caused by the hydrofluoric acid-based chemical cleaners for masonry. Etched glass usually requires full replacement of the affected pane.
1.03 SYSTEM DESCRIPTION
- A window glass in proper condition is free from streaks of dirt from rain water combined with atmospheric impurities.
NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).
- Washing liquid - washing soda (Arm & Hammer, no ammonia if hardware is bronze).
- Household Ammonia: CAUTION: DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, A POISONOUS GAS WILL RESULT! DO NOT USE BLEACH ON BIRD DROPPINGS.
- A weakly basic compound that is formed when ammonia dissolves in water and that exists only in solution.
- Other chemical or common names include Ammonia water*; Ammonium Hydroxide; Aqua ammonia*.
- Potential hazards: TOXIC; MAY IRRITATE THE EYES.
- Available from chemical supply house, grocery store or pharmaceutical supply distributor, or hardware store.
- Household Vinegar
- Commercial Window Cleaner - non-alkaline (without ammonia if hardware is bronze).
- Fine pumice, commercial whiting or old hardwood sawdust used as a scouring powder to clean and polish glass in combination with a commercial liquid window cleaner - use this for stubborn dirt only.
- Clean, potable water
- Heavy gloves and protective gear
- Very fine 0000 steel wool
- Pliers and chisels
- Sponges, natural or artificial, window washer tools, squeegee
- Soft bristle brush
- Clean, soft cloths
- General Cleaning of Glass:
- Brush surfaces with a soft bristle brush to remove abrasive dust and oil films which build up on the glass. These contain sharp dust particles which can scratch and degrade the glass.
- Wash the glass with a solution of nonsudsing household ammonia in water, -OR- vinegar in water.
- If the above procedure does not sufficiently clean the glass, apply commercial window cleaner and wash (starting at the top of the window) with natural or artificial sponge, or with window washer tools.
- Use straight overlapping strokes and wash from side to side.
- Wet the window thoroughly and use a wooden scraper with an up and down stroke to removestubborn spots. Take care not to apply any pressure to the glass.
- If dirt is still stubborn, combine window cleaner with fine pumice, commercial whiting, or old sawdust to clean and polish glass.
NOTE: DO NOT APPLY PRESSURE, AS THIS CAN ETCH THE GLASS.
- Wipe down painted metal components with metal cleaner. Rinse off immediately and dry.
- To dry the glass:
- Wet the side of the squeegee and pull it across the window.
- Wipe the squeegee blade with a wiping cloth after each pull. Wipe corners of each pane.
- Pick up water from the corners with the sponge braced with one finger. Wipe edges with a wiping cloth if necessary.
- For discoloration, wash the glass with a non-ionic detergent and very fine 0000 steel wool. DO NOT APPLY TOO MUCH PRESSURE - IT WILL BREAK THE GLASS OR SCRATCH THE SURFACE OF THE GLASS.