Pane Clinic

Do you think the home builders of 1776 used multi-paned 6 over 6, and 9 over 9 double-hung windows because of their darling decorative demeanor?

Nope.  Limits of technology.

Due to the difficulty of making LARGE distortion-free pieces of glass, a large window required a carpenter to construct a grid of intricately intersecting mullions, to hold an assembly of SMALLer panes.

And even SMALL panes had optical distortions.  A glass blower created either a sphere or a cylinder, slit and flattened it onto a capping table, and finally cut the cooled glass into panes.  Flattening the glass caused the distortions.  Even so, and in spite of the cost, glass was in high demand, a miracle product, able to admit light while excluding the weather.

If they could have had larger panes, say 3 foot x 3 foot, they'd have been THRILLED.  Fewer mullions = less carpentry, and less puttying and painting.

Historical Societies assign nobility to the old.  Older = better, though from a technological standpoint, that's almost NEVER true.  But people like traditional looks.  Utilizing modern technology, today's window manufacturers easily produce 3 foot x 3 foot panes, and substitute less expensive fake mullions to satisfy the public's taste.   And don't forget the faux shutters ! 

Heck, today you can have a perfect distortion-free sheet of glass 12 feet wide x 40 feet long, [unless you have a longer trailer].  But try to slip THAT past a persnickety Architectural Review Board !!