Sash windows have been a popular design method going back over 300 years. Their simple beauty and functionality have been developing since the 16th century when they were first introduced. The original designs were built into the wall in such a way that they were flush with the outer wall, creating a very visible and aesthetically beautiful display. After time, due to many considerations (not the least of which was the ease of dislodging such a design from it's setting) regulations were put in place requiring sash windows to be recessed into the wall. This was further developed into where the 'sash-box', the part where the mechanism for controlling the rise and fall of the window is contained, was recessed into the wall as well.
The shape of a sash window can refer either to it's overall design, which can vary wildly (though it is almost without exception rectangular in shape), but also down to the shape and design of the muntins that are found between each individual pane of glass. These come in a variety of forms, from the wide and shallow forms of the Ovolo design, to the narrow and pointed lamb's tongue.
The 19th century saw the introduction of an entirely new style of sash window. There was experimentation trying to step away from the older grid style to something more innovative and attractive. It was during these time periods that colored panes started to be included, and narrow, wedge shaped pieces of glass were worked into hemi-spherical tops to the windows. During this time the windows also started to increase in size, sending light flooding into grand rooms where the upper class gatherings and salons of the period gathered.
This is just a bit of the history of the wonderful world of sash windows, and a few of the myriad of shapes, styles, and sizes that have been seen since they first appeared 300 years ago. There are many more that have been seen all over the world since then, so before selecting a sash window for your home, dig into this interesting design!