Shingling was a stage in the production of bar iron or steel, in the finery and puddling processes.
In each case, this needed to be consolidated by hammering it into a more regular shape.
The result was an oblong-shaped iron product similar in appearance to shingles used on roofs.
In the finery, this was part of the work of the finer; during puddling, it was done by a special workman called the shingler.
In more recent times, the process was carried out using mechanical jaws to squeeze the puddled ball into shape.