Hi wlk,
Thank you for a very interesting question. Please be aware that
wrought iron is frequently coated with lead based paints, often with a
75% lead content. Care must be taken in restoration.
The first part of my answer begins with the history of wrought iron,
on to detailed information regarding identification, repairs,
dismantling, cleaning, reassembly and protection, and lastly
maintenance.
Following that, I've included a link for a video from Home & Garden
television which demonstrates repair techniques along with explaining
the importance of keeping hand-wrought items clean, sealed and dry.
The most detailed information about wrought iron gates and railings
can be found at: The Wrought Iron Advisory Centre:
http://www.realwroughtiron.com/wiac.htm
HISTORY
"Wrought iron has been used in building from the earliest days of
civilisation, wrought iron door furniture being commonplace in Roman
times. The structural use or iron dates from the Middle Ages, when
bars of wrought iron would be used occasionally to tie masonry arches
and domes."
[edit]
"By the turn of the century this had led to buildings completely
framed in wrought iron, and later steel, girder sections, and cast
iron was once again relegated to an ornamental role.
Our main concern with wrought iron, however, will be in its
application to gates and railings, frequently given an ornamental
treatment by the blacksmith. There are wrought iron railings in
Westminster Abbey from the thirteenth century, which, in essence
display all the characteristics which we have come to know as ~
'wrought ironwork', although lacking modern refinements such as
symmetry and sweetness of line, but the great age of British ironwork,
known as the English style began at the end of the seventeenth
century. A French fashion for the Baroque style in gates and railings,
swept the country houses of Britain, following the import of craftsman
by William and Mary, and the greater part of our national stock of
good ironwork dates from the early years of the eighteenth century.
After the rise of cast iron as an ornamental medium, wrought iron
tended often to take a secondary role, owing to its comparative
expense, each piece being made by hand, while castings could be
repeated ad infinitum, once the patterns were made. Technically,
however, the craftsmen of the age of machines, excelled their
forebears, as indeed they must while making mechanical components, so
that the ornamental blacksmith work of the nineteenth century displays
a perfection of manufacture not seen before nor since
After the introduction of mild steel, cheap because of its ability to
be mass produced, wrought iron, and the craft skills associated with
it, gradually disappeared in accordance with the general decline of
craft standards in the twentieth century, until the last ironworks
ceased production in 1974."
[edit]
IDENTIFICATION
"Wrought iron is unlike cast, in that it is not brittle, and seldom
breaks. For this reason, wrought ironwork is frequently far more
delicate, although years of paint can obscure this. Cast iron is most
frequently identified by its repetitive nature, and forms, which could
be carved in a wooden pattern, but not made by hammer and anvil.
Telling wrought iron from mild steel is often more difficult, as both
will bend, and not break Frequently, however, work in mild steel is
readily identified by the lower standards of workmanship often used.
Look for evidence of electric welding Also mild steel is often given
away by more active corrosion, which tends to run out of the joints in
a steel gate, and stain the paintwork, where this is seldom the case
with wrought iron. Wrought iron may also be dated, approximately by
its texture. Until the very end of the eighteenth century, sections of
wrought iron were derived by forging of billets by hand or water
power, this resulted in a more or less uneven surface texture, and
very sharp corners. A foreshortened view of a bar displays well the
irregularities of the surface. Rolled bars, on the other hand,
produced from the beginning of the nineteenth century, are perfectly
smooth, and the corners can display a small radius. Nineteenth century
wrought iron is known as 'puddled iron'."
ALTERNATIVES
"The modern replacement for wrought iron is mild steel. Many
metalworkers are perfectly content to use this much cheaper metal both
for new work and the refurbishment of old. I would like to suggest the
reasons why this is not acceptable, while wrought iron is yet
available.
1. The weathering properties of wrought iron are well known. While it
does of course rust in time; with reasonable maintenance this can
indeed by a very long time.
The fact that so much ornamental work survives from three hundred
years ago says a lot for the material. On the other hand, steel is
well known for its corrodability, and the intricate forms and water
traps of 'wrought ironwork', only encourage corrosion. Hence it is
normal practice to coat steelwork with zinc, which does indeed delay
corrosion, but neither galvanising nor zinc spraying can effectively
be applied to complex forms.
2. Modern conservation practice insists on the replacement of
materials with like materials. When wrought iron is available for the
repair and replication of wrought ironwork, why use mild steel?"
[edit]
MAINTENANCE
"Ironwork is commonly supposed to be nearly free of maintenance.
Unlike wood work which is religiously subjected to a stern regime of
regular painting, ironwork is frequently left to rust undisturbed for
long periods, so much so that the only attention that much even
important ironwork receives, is periodic major overhaul, at great
expense. This could be avoided by frequent small attention. Insistence
on frequent inspection would be of benefit, perhaps once a year, with
immediate, and usually trivial remedial work to arrest any developing
problems."
[edit]
WROUGHT IRON - TECHNIQUES OF RENOVATION.
"There are two types of wrought iron. The irons of antiquity, now
known collectively as "charcoal iron", and a mass-produced iron,
produced in the 19th century and early 20th century, known as "puddled
iron". Although pre-18th century wrought ironwork is, of course
composed of charcoal iron, it is normal to make repairs and
replacements in Puddled iron, owing to its similar properties. On no
account should mild steel be used on external work without zinc
coating by galvanising or hot metal spraying. As neither of these
treatments is permissible nor effective with ancient work, the use of
mild steel is effectively ruled out.
Removal From Site.
Most work is ideally carried out in workshop conditions, and it is
frequently the case that iron components can be removed easily from
site. In the case, however, of railings, gate Piers etc which may be
fixed into stonework, usually in lead~filled sockets, removal may not
be possible without sacrificing expensive stonework. Lead may be
removed from sockets by mechanical means, but this is very laborious
and any attempt to melt the lead will inevitably result in failure,
and damaged stonework unless the Socket can be held horizontally to
enable the lead to run out.
Cleaning
Ironwork is generally covered in paint and frequently a build-up of
rust in water traps etc. Commonly, paint and some of the rust are
removed by grit blasting. There are, however good arguments against
grit blasting, as follows, so that it should be regarded as a last
resort.
Grit blasting will remove the outer surface of the iron, known as mill
scale. This mill scale, which is typically 90% intact on work 300
years old or more, is the original surface to which paint was applied,
and as such is as worthy of conservation as the rest of the iron.
Further, the mill scale, in such a case has a proven record of keeping
corrosion at bay. It is a protective surface in its own right, and
hence of value. Further still, grit blasting will render all of the
iron surfaces the same, thus removing permanently any evidence which
may be present on the surface of the iron. For example, a component,
which has been renewed, and is thus not original, will exhibit a
different colour of mill scale to the original. It is often the case
that successive generations of repair can be detected, on the basis of
colour alone. A surface which was originally polished for, say, indoor
use, may still retain its bright appearance, under the paint, giving
us evidence, perhaps of a former use. Likewise, file marks etc, giving
evidence of techniques of manufacture, will be removed by grit
blasting.
Where possible, we will always recommend paint stripping by chemical
means, with a thorough removal of the chemical agents, usually by
steam cleaning. This will result, for the most part in the restoration
of the piece to its original appearance as it was immediately prior to
painting. Rust deposits are normally dealt with by the application of
heat. Rust scale does not expand when heated to the same extent as
does the iron. The differential in expansion causes the rust to lose
its grip, when it may be shaken or brushed off. Heating the area to a
red heat also results in the reduction of the surface layer of the
metal to a consistency similar to mill scale. Often, where there has
been a considerable accumulation of rust, the application of heat is
needed anyway as part of the remedial process. (SAFETY NOTE: Wrought
iron is frequently coated with lead based paints, often with a 75%
lead content. Care must therefore be taken, particularly with grit
blasting, to ensure that both operatives and the public are protected
and that the lead working regulations are adhered to).
Dismantling
Ironwork is often fastened together with riveted, or tenoned joints.
It is not possible to part such joints without at least some damage,
or weakening becoming evident on re-assembly. It is worth avoiding the
parting of frame joints etc, merely to gain access to corroded
components, as the frame will never be as strong again. Where tenoned
joints must be parted, it is nearly always necessary to replace the
tenon with a screw or screwed tenon, in order to gain adequate
strength.
Repairs and Replacements
As a matter of course, the replication of components should be carried
out in a manner similar to that which was used for the original
creation of the piece, and in similar materials. Ideally, all work to
an ancient piece should use the old techniques of forge welding,
tenoning, riveting and collaring etc. so that a high degree of
blacksmithing skill is generally required.
However, it is often the case that components cannot be completely
removed from the job, or that only small work is need to a large
component. In this case, recourse must be taken to more modern
techniques.
For structural purposes, where part replacement is required, as, for
example in the case of a gate backstile, which may be rusted away at
the bottom, arc/mig welding is used to join on the new part. No
special equipment is required for the electric welding of wrought
iron, only that normally used for the welding of mild steel; however,
mild steel electrodes or MIG wire are not acceptable, a ferrous
non-corrodable alloy must be used. Care must be taken in preparation
however, as wrought iron is a laminar material, and welding must be
carried out through the full depth of the section. Attaching
components to the surface of wrought iron sections is not very strong.
Alternatively, gas welding or brazing may be used, and are often
useful for the attachment of components such as waterleaves, where the
original method of forge welding or riveting cannot be done.
Sections which are heavily pitted, or wasted, but which are still
structurally sound, may be repaired by the puddling in of new wrought
iron, in the form of thin rods by the gas welding process. Iron thus
deposited has no laminar structure, and hence little tensile strength,
but otherwise appears to exhibit the properties of the parent metal.
Alternatively, these sections can be built up by electric welding, but
again use must be made of a suitable alloy. Care should be taken to
avoid distortion of any section so treated.
Sheet work, such as leaves, being often impossible to access for the
painting of both sides, is the usual candidate for replacement. For
many years, there was no commercially available supply of iron
suitable for the often-deep distortion necessary in repousee work.
Copper was often used, but it is soft enough to be easily bent, and
will not hold paint well, while mild steel, particularly in thin sheet
form will soon rust away."
[edit]
"It must be said that often, the repousee leafwork found on ancient
work, is of such a high standard of craftsmanship, that one cannot
hope to accurately replicate it. In this case, we often make a point
of preserving, at all costs, at least one of the originals, in order
to give future students at least a clue. When a piece of sheetwork is
reduced virtually to lace, it may still be conserved, by scrupulous
cleaning and the application of a layer of epoxy-resin to the rear
surface. The detail can then often be restored by careful carving into
any resin protruding on the front surface, with files etc.
Reassembly
"The most common reason for the rusting of wrought ironwork, is the
gathering of water in places which will not dry. Wrought iron will
last indefinitely, with reasonable maintenance, if rainwater is kept
at bay."
[edit]
Protection.
"Galvanising and zinc spraying have been mentioned, There are good
reasons why these will not do. Galvanising depends upon dipping the
work, after cleaning in acid, in a bath of molten zinc, which leaves a
rather thick layer of zinc on the surface. Drips frequently form which
must be ground off. Wrought iron is often etched very deeply by the
action of the process. If you add to this that the small joints will
remain full of acid after the treatment, it is easy to see why this
process is not appropriate to delicate and complex wrought ironwork.
(Additionally, in certain circumstances, the galvanising process can
deeply etch the surface of wrought iron causing irreversible damage to
the piece.)
Zinc spraying is a far less brutal process. It is a hand method, which
consists of removal of all mill scale by grit blasting, and the
immediate application of a zinc coating with a type of flame gun. The
objections to grit blasting have been enumerated above. Further, it is
not possible to clean very small joints by grit blasting, from the
physical restrictions imposed by the size of a grain of grit, neither
is it possible to clean nor spray material which is not accessible to
line of sight. The water traps in wrought ironwork are just such small
joints and out-of-the-way places.
Owing to the natural ability of wrought irons to resist corrosion, by
reason of their in-built barriers of slags, it is sufficient to
protect ironwork by a good coating of paint. However, I cannot stress
too strongly that, in common with other items placed out of doors,
such as woodwork, wrought ironwork needs regular maintenance. Chips
and developing problems should be dealt with at the earliest dry
opportunity, and the work should be painted at least every five years.
NOTES ON MAINTENANCE OF WROUGHT IRONWORK
Suggest the establishment of a rolling programme of maintenance, of
all items of ironwork, based upon the following schedule.
1. Initial attention in the form of repair or restoration.
2. Annual inspection, both rigorous and minute, of every detail of
ironwork. Look particularly for signs of rust seeping from, or water
lodging in joints. Any chipping of well-ventilated areas is not too
significant.
3. Attend to any problems at the earliest opportunity, but only in
periods of warm and dry weather when joints can thoroughly dry out.
Any rust scale should be removed, preferably by local heating.
4. Try injection of low viscosity, oil based rust inhibitor into
joints, followed by resealing of damaged areas by touch-up paintwork.
5. Thoroughly re-paint ironwork periodically, but at most five-yearly.
6. Long term plan for stripping of accumulated layers of old paint,
accompanied by any repairs. Stripping preferably by purely mechanical
and chemical means, rather than by grit blasting, which removes the
iron's own original protective layer of oxide.
THEN BACK TO
1. Again et cetera ad infinitum"
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Home & Garden Television - Care for Wrought Iron
http://www.hgtv.com/cr/cda/article_print/1,1250,HGTV_3716_1377946,00.html
"Wrought-iron railings and banisters are typical in country decor. In
the video below, Country Care expert Bruce Johnson demonstrates repair
techniques and explains the importance of keeping hand-wrought items
clean, sealed and dry."
(On the right side of page you'll see a photo with an explanation:
"The number-one enemy of wrought-iron items such as this light fixture
is moisture." Click below that photo where you see
"REAL VIDEO
How to clean and protect wrought iron"
You'll be able to view an explanatory video regarding cleaning and
protecting wrought iron.
Please note:
To view videos on HGTV.com, you must use a Windows Media, QuickTime,
or RealOne video player. It?s likely you already have one of these
players installed in your computer system. If not, download and
install any one of the following media players.
Windows Media: http://www.windowsmedia.com/mg/home.asp
QuickTime: http://www.apple.com/quicktime
RealOne: http://www.real.com/index.html
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The Wrought Iron FAQ's
http://doityourself.com/clean/wroughtiron.htm
"Wrought iron is used for decorative items. It is generally made out
of the purest form of iron, thus is somewhat more resistant to rust
than cast iron.
A protective coat of liquid wax will make cleaning easier and retard
rusting. Do not use liquid wax on fireplace accessories because it is
flammable. When needed, wash with a damp cloth and wipe dry.
To remove rust stains, rub with kerosene, and scour with fine grade
steel wool. If rust is difficult to remove, allow kerosene to remain
long enough to loosen. Commercial rust removers may also be used."
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Best regards,
tlspiegel |
