Although it might be thought that the main changes from pre-Revolutionary to Revolutionary times in the British Colonies in North America were cultural and political, and that this would have little impact on the designs of old eyeglasses from this period, there was in fact a notable alteration in the way spectacles were made as the two eras succeeded each other. Thus, it is possible to easily distinguish Colonial and Revolutionary eyewear despite their many similarities.
This period of time is bridged, as it were, by the life of one famous man – Benjamin Franklin – who made one of the most remarkable American contributions to the science of spectacles. He was the first to fit old eyeglasses with bifocal lenses.
The concept appears to have been his own original idea, so this period witnessed an advance in lens manufacture that is still very important and prevalent today. Therefore, any discussion of the period must take Franklin's influence as an innovator of old eyeglasses into account, as well.
Changes in the shape of old eyeglasses' lenses and eyerims
For the first few centuries of their existence, the lenses used in antique eyeglasses were almost universally round. The perfectly circular shape made it technically and mathematically easier to create a lens with the proper focal characteristics, given the techniques and materials of the day. Of course, it was still a painstaking process that required an impressive amount of skill, since each lens needed to be ground by hand, with constant testing of its power, to achieve the proper strength in “pouces”, “inches”, or the other local measurement of optical effectiveness.
Round lenses are mathematically simpler to grind correctly (though still very complex), so it is only natural that during the formative centuries of eyeglass manufacture, skilled artisans should stick very close to this tried and true method of producing high quality lenses. Why undergo the difficulties of making oval lenses when round ones were easier and provided adequate vision correction?
Yet the transition from pre-Revolutionary to Revolutionary period vintage eyeglasses shows the mute declaration of a sudden improvement in techniques, in the form of many lenses which were no longer perfectly round. The grinding methods and understanding of optics both improved in this period to the point where making oval and octagonal lenses was an attractive proposition to lens grinders and frame makers who needed to risk their own incomes and effort with this new approach.
Oval and octagonal lenses
Both oval and octagonal lenses appear during this period, which is a major change from the old eyeglasses used in the 17th century. Round spectacles naturally continued to be made (they are, after all, still made today), but horizontally elongated shapes became so common that many collections consist mostly of these, with few or no round Revolutionary period old eyeglasses to be found among them.
Octagonal glasses are almost rectangular, though with slanting corners which turns them into stretched octagons instead. Both ovals and octagons offer a wider field of view to the wearer. With 1” wide round lenses, it is necessary to focus directly forward to gain the benefit of the spectacles, but with the horizontal extension of ovals or octagons, the wearer can take in a larger view with full optical assistance just by moving their eyes, rather than needing to turn their whole head.
The presence of oval or octagonal lenses marks a pair of old eyeglasses as belonging to the last years of the pre-Revolutionary period or as being from the days of the Revolution. There are other signs as well, which will be examined further in articles that follow.