Page 126 - The Building Conservation Directory 2013

1 2 6 t h e b u i l d i n g c o n s e r vat i o n d i r e c t o r y 2 0 1 3 T w e n t i e t h a N N i v e r s a r y e d i t i o n
3.3
Structure & Fabric :
Metal,
Wood & Glass
only become visible once the window has
dried completely.
The safest and most effective way to
clean historic windows that have no painted
decoration, or where the decoration is in
sound condition, is to roll (not rub) cotton
buds dampened with a little de-ionised water
over the glass surfaces. The slightly damp
cotton fibres collect the dirt from the surface
very effectively. Cotton buds of the required
size can be made quite easily using bamboo
skewers and raw cotton, which is available
from most pharmacies. This enables the
cotton buds to be rolled to suit the size of the
piece of glass to be cleaned.
On unpainted glass, once the cotton bud
has stopped collecting dirt, a final polish
can be carried out to help the glass regain its
brilliance. It is always inadvisable to polish
painted glass.
In exceptional circumstances, for
example where dense rust staining (previous
page, bottom right) has caused unsightly
discolorations on plain glazing, more abrasive
methods like bristle brushes and plastic pot
scourers may be used as a last resort, but only
after taking professional advice.
Damage caused by cleaning
The surface of glass is surprisingly prone
to scratches. It is quite wrong to assume
that only diamonds are hard enough
to scratch glass: wire wool, glass-fibre
brushes, abrasive powders and metal
tools can cause serious damage. While
the damage may not be immediately
visible, very small scratches can cause
corrosion, particularly in medieval glass.
The removal of corrosion deposits on
medieval glass is controversial, because over-
cleaning can expose very fragile corroded
glass surfaces. Cleaning of corroded glass
should only be attempted by appropriately
trained, skilled and experienced conservators,
and should be done in moderation. A
corroded window will never look as good as
new, nor should it. Time has left its mark and
that change is part of the window’s history.
Over-cleaning of windows that
have fragile paint can result in severe
and irreversible damage, such as the
loss of painted detail, and can leave a
window unreadable. Unlike paintings
on canvas or paper, it is very difficult
to touch-in lost glass paint.
Dos and Don’ts
Cleaning can improve the legibility and help
the long-term survival of a window, but it
must be done carefully and correctly.
Do seek the advice of an expert before
deciding to clean a window. It is always
worth getting good advice at the start –
once damage is done it cannot be undone.
For churches, the local diocese can often
help by recommending an advisor who
specialises in stained glass. Icon, the Institute
of Conservation, has a searchable online
register of accredited conservators (www.
conservationregister.com).
Do provide safe access. Church windows
tend to be tall and are often at great height.
Safe access is important; it’s not worth risking
injury or worse for a clean window.
Don’t use harsh abrasive pads or
household cleaners and never use acids or
wire wool. Even the removal of cobwebs
should only be done extremely carefully and
the duster should never touch a window that
contains painted stained glass.
Don’t attempt to clean medieval stained
glass if you are not a trained and experienced
stained glass conservator.
And finally: if in doubt, don’t clean.
A Henry Holiday window in St Mary’s Church before and after cleaning
Details of one of the Henry Holiday windows before and after cleaning