Modern painted railings at Bessborough Gardens, Pimlico
"In the first half of the nineteenth century 'invisible' greens (so called because they would blend into a background of foliage) were used for fences, gates, railings and garden furniture. In 1840 [sic] Humphrey [sic] Repton recommended a 'bronze' finish, made by powdering copper or gold dust on a green ground. Green was used throughout the mid-Victorian period but dark blue, red and chocolate brown were also popular."The Victorian Society.
Choosing a paint finish for restored traditional ironwork can be tricky, as iron railings were traditionally painted with lead-based paint.
The question was discussed at at the Traditional Paint Forum conference in 2009. At the conference Geoff Wallis from Dorothea Restorations explained how iron interacts with oxygen and water and how a painted coating like lead helps protect the iron and prevent corrosion. And paint consultant Patrick Baty described how early iron work was painted a 'lead' or 'iron grey' using lamp black as a pigment.
Later developments led to Prussian Blue as a colouring. A 'smalt' pigment, coloured by the use of cobalt, created another fashionable but expensive blue paint. Later on, 'Invisible Green' was a popular choice for painted railings. However, with the introduction of chrome yellow came the possibility of making brighter greens. A 'bronze green' was used extensively throughout the nineteenth century.
Lead has been used since ancient times as a paint pigment for ironwork. Two major chemical forms of lead are used as colours: "white lead" (a lead carbonate) and "red lead" (a lead oxide).
Red lead and red oxide were discovered to be effective in protecting against corrosion. Both types of lead provide a thick, heavy, tough coating that does not crack through wear or temperature variations, as it expands and contracts in unison with the base metal to which it is attached. Because of these properties, lead paints continue to be widely used for large metal structures like bridges.
While there would often be a preference for the retention of historic paint, this does not always make for the best substrate for modern paints. Modern alkyd paints can delaminate and many experts consider that the performance of modern gloss paints remains inferior to that of lead-based paints.
However, concern over the potential hazards of using lead continued to grow and, when titanium dioxide became available in commercial quantities in the mid 20th century, it soon started to replace white lead.
By 1970 the use of white lead in decorative paints was voluntarily withdrawn by the paint industry and in 1992 its use was prohibited except for approved applications on Grade I and II*-listed buildings (Grade A in Scotland), and their use is monitored by English Heritage, Cadw and Historic Scotland. Information on the requirements can be obtained from these bodies or from the white lead paint manufacturers.
Modern railings are now largely painted black (or sometimes green). One theory is that this is replicating railings painted black following the death of Prince Albert. At the conference Mr Baty said it was more likely that black was a popular choice as the fastest drying of the modern alkyd paints in the post-war period.
Deciding how to balance retention of the original appearance with a low maintenance requirement is tricky; but where the appearance is of over-riding importance for listed structures, experts will often chose a lead-based oil paint, which will at least degrade more sympathetically than modern paints.
Ironwork well maintained will last for many, many years. The loving and painstaking restoration of so much high-quality iron work has been one of the most popular and visible improvements in our streetscapes, squares and parks in the last decade or so.