This is one of the first occasions in which an optical innovation affected the very appearance of the frames.As our illustration shows, the new style could apply to the older type of nose spectacles as well as the newer type of wig spectacles.As such it was used in various manufacturing industries as a forerunner of plastic, for example to strengthen parasols.Reinforced corsets might be described by their wearers as 'prisons of whalebone' but we like to think the owner of these spectacles was glad to wear them.At some point in the century, possibly as early as the 1760s London opticians began producing split lenses.
At the turn of the century John Yarwell could advertise lenses ‘set neatly in Leather, Horn, Silver or Tortoise-shell Frames’, though tortoiseshell was not to be really popular for another two generations.
Note how this rough Nuremberg type (1700-1750) still present at the start of the century gave way first to an improved steel spring variety of nose spectacles (with centrally-hinged bridge, dating from perhaps c.1740) and eventually a recognisably modern spectacle frame made from a single material, in this case steel, from c.1760. Instead of just being classified roughly as for 'old' or 'young' sight they were provided in a range of optical powers.
The focal length (in inches) might be marked on the spectacle side.
The other material most commonly observed in the surviving specimens is iron. The process of making crucible steel had been developed by the Sheffield watchmaker Benjamin Huntsman in 1742 and various other kinds were available prior to the development of the standard Bessamer Process in the 1850s. Whalebone is a rare material to encounter in antique eyewear and the museum is lucky enough to possess two examples, one an eighteenth century pair with sides.
Spectacles proved to be a particularly apt application for this light-weight but strong material. This frame dates from around 1750 and you may be able to see that the whalebone has been welded as two strips and tied at the bridge after the insertion of the lenses.