Metals such as aluminium and copper were indeed scarce and were presumably re-cycled. Railings were of little value and were frequently dumped into the Thames!
This information came from dockers in Canning Town in 1978 who had worked during the war on 'lighters' that were towed down the Thames estuary to dump vast quantities of scrap metal and decorative ironwork. They claimed that so much was dumped at certain spots in the estuary that ships passing the area needed pilots to guide them because their compasses were so strongly affected by the quantity of iron on the sea-bed.
Now That the war has long since passed we offer the service of replacing your Railings to restore your London property to its former glory.
Please browse through the site and see if there is anything of interest.
Railings used to be painted all sorts of colours. The Victorian Society says on their website
that: "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 Humphrey 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."
Following the death of Prince Albert in 1861, iron railings (as well as doors, window frames and just about anything else you could think of) were painted black as a sign of mourning. In these times, under a monarch that mourned her husband's passing for years to come (and famously continued to wear black until she too passed away), it should come as no surprise that the railings remained black for many decades following Prince Albert's death.
When and where railings were (eventually) replaced after WWII, an unconscious effort appears to have been made to restore London to its exact former state, meaning that the new railings were also painted black.