By Chris Topp
Wrought ironwork is the product of the blacksmith, and a smith should be asked to do the work. Much ornamental work was done by smiths of exceptional ability, and we strongly recommend seeking out a specialist to obtain good work. The aim should be to put the ironwork back to its original condition, if possible, and it’s worth spending the extra to get work which respects the original, and this means using original techniques and materials wherever possible.
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. Mild steel, as it corrodes very quickly out of doors, should on no account be used on external work without zinc coating, 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.
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 evidence, perhaps of a former use. Likewise, file marks etc, giving evidence of techniques of manufacture, will be removed by grit blasting.
Where possible, paint should be stripped 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.
Often there will be components which have corroded beyond use, or which have simply gone missing, and, as a matter of course, the replication of components should be carried out in a manner identical 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 a small area of work is need to a large component so that recourse must be taken to alternative techniques. More often than not it is a good idea to avoid too much dismantling, so that replacement elements must be attached to existing work. There are modern techniques which are appropriate such as electric welding and brazing, and it is the work of the specialist to decide which are most appropriate.
The watchword within conservation is ‘reversible’, meaning that whatever you do should be capable of being undone. This applies particularly to paint finishes, where many modern solutions, such as epoxy paints and powder are not easy to remove and thus not ideal. The preservation of ironwork is best accomplished by using oil based traditional paint systems. As long as competent materials have been used in the repairs, the natural resistance to corrosion of wrought iron obviates the need for sophisticated protection. There should be at least four coats of paint, applied over the natural mill scale, and the water traps should be well filled with paint or resin, as these are the places where corrosion will start. Most important is a commitment to maintenance, wrought ironwork should be repainted as often as exterior woodwork, and if this is done there is no reason why it will not be in good condition a century from now.
This article first appeared in Listed Property Owners Club magazine July /August 2010
Chris Topp & Co Ltd is a 30 year old company, based in North Yorkshire which is the only producer in the world today of genuine wrought iron and a leader in the restoration of heritage ironwork. They are one of the best known names for the design and creative production of modern and traditional iron work.