Cleaning historic glass
This procedure includes guidance on cleaning glass in existing windows. Italso 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 weathercauses
surface crazing and alkalinereaction opalescent films if
not washed at least every severalyears.
B. Discoloration is an oily film on the surface ofthe
glass. It is caused by oil, coal,and other fossil fuels
existing in the atmosphere, bymagnesia dioxide photo-
oxidizing in the glass under strongultra-violet light,
or by the addition of excessivealkali salts to produce
a colorless product.
C. Etching is scratching of the glass produced byvigorous
cleaning, steel wool, abrasivepapers, or kitchen
scouring compounds. Etchingcan occur on windows that
have been exposed to wind blowngrit, or left unprotected
during sandblasting of masonrybuildings. Etching can
also be caused by the hydrofluoricacid-based chemical
cleaners for masonry. Etchedglass usually requires full
replacement of the affected pane.
1.03 SYSTEM DESCRIPTION
A. A window glass in proper condition is free fromstreaks
of dirt from rain water combinedwith atmospheric
NOTE: Chemical products are sometimes sold under a common
name. This usually means that the substance is not as pureas
the same chemical sold under its chemical name. The gradeof
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 AMMONIAWITH CHLORINE BLEACHES, A
POISONOUS GAS WILL RESULT! DONOT USE BLEACH ON BIRD
1. A weakly basiccompound that is formed when ammonia
dissolvesin water and that exists only in
2. Other chemical orcommon names include Ammonia
water*;Ammonium Hydroxide; Aqua ammonia*.
3. Potential hazards: TOXIC; MAY IRRITATE THE EYES.
4. Available fromchemical supply house, grocery store
orpharmaceutical supply distributor, or hardware
C. Household Vinegar
D. Commercial Window Cleaner - non-alkaline (withoutammonia
if hardware is bronze).
E. Fine pumice, commercial whiting or old hardwoodsawdust
used as a scouring powder to cleanand polish glass in
combination with a commercialliquid 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 washertools,
E. Soft bristle brush
F. Clean, soft cloths
A. General Cleaning of Glass:
1. Brush surfaces witha soft bristle brush to remove
abrasivedust and oil films which build up on the
glass. These contain sharp dust particles which
canscratch and degrade the glass.
2. Wash the glass witha solution of nonsudsing
householdammonia in water, -OR- vinegar in water.
3. If the aboveprocedure does not sufficiently clean
theglass, apply commercial window cleaner and wash
(startingat the top of the window) with natural or
artificialsponge, or with window washer tools.
a. Use straight overlapping strokes and wash from
b. Wet the window thoroughly and use a wooden
scraperwith an up and down stroke to remove
stubbornspots. Take care not to apply any
pressureto the glass.
4. If dirt is stillstubborn, combine window cleaner
withfine pumice, commercial whiting, or old
sawdustto clean and polish glass.
NOTE: DO NOT APPLY PRESSURE, AS THIS CAN ETCH THE
5. Wipe down paintedmetal components with metal
cleaner. Rinse off immediately and dry.
6. To dry the glass:
a. Wet the side of the squeegee and pull it
b. Wipe the squeegee blade with a wiping cloth
aftereach pull. Wipe corners of each pane.
c. Pick up water from the corners with the sponge
bracedwith one finger. Wipe edges with a
wipingcloth if necessary.
B. For discoloration, wash the glass with a non-ionic
detergent and very fine 0000 steelwool. DO NOT APPLY
TOO MUCH PRESSURE - IT WILL BREAKTHE GLASS OR SCRATCH
THE SURFACE OF THE GLASS.
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