Cleaning Historic Glass
CLEANING HISTORIC GLASS
A. 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.
A. Dirt accumulations on glass exposed to weather causes
surface crazing and alkaline reaction opalescent films if
not washed at least every several years.
B. 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.
C. 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. A window glass in proper condition is free from streaks
of dirt from rain water combined with atmospheric
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 (*).
A. Washing liquid - washing soda (Arm & Hammer, no ammonia
if hardware is bronze).
B. Household Ammonia:
CAUTION: DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, A
POISONOUS GAS WILL RESULT! DO NOT USE BLEACH ON BIRD
1. A weakly basic compound that is formed when ammonia
dissolves in water and that exists only in
2. Other chemical or common names include Ammonia
water*; Ammonium Hydroxide; Aqua ammonia*.
3. Potential hazards: TOXIC; MAY IRRITATE THE EYES.
4. Available from chemical supply house, grocery store
or pharmaceutical supply distributor, or hardware
C. Household Vinegar
D. Commercial Window Cleaner - non-alkaline (without ammonia
if hardware is bronze).
E. 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.
F. Clean, potable water
A. Heavy gloves and protective gear
B. Very fine 0000 steel wool
C. Pliers and chisels
D. Sponges, natural or artificial, window washer tools,
E. Soft bristle brush
F. Clean, soft cloths
A. General Cleaning of Glass:
1. 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.
2. Wash the glass with a solution of nonsudsing
household ammonia in water, -OR- vinegar in water.
3. 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.
a. Use straight overlapping strokes and wash from
side to side.
b. Wet the window thoroughly and use a wooden
scraper with an up and down stroke to remove
stubborn spots. Take care not to apply any
pressure to the glass.
4. 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
5. Wipe down painted metal components with metal
cleaner. Rinse off immediately and dry.
6. To dry the glass:
a. Wet the side of the squeegee and pull it
across the window.
b. Wipe the squeegee blade with a wiping cloth
after each pull. Wipe corners of each pane.
c. Pick up water from the corners with the sponge
braced with one finger. Wipe edges with a
wiping cloth if necessary.
B. 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.
END OF SECTION