The layout of an Italiante window pediment

  9/14/25: my last diagram is not quite right. I will update it.

 

The curvy Italianate molding above that window in the center?  How did they do that? 

How did carpenters in south eastern Massachusetts in c.1850 lay out the picturesque pediment so it could be cut and assembled?  

 

 

This was the question posed to me by Nathan Goodwin of H.I.S. Construction. He was asked to lay out a copy of that molding for installation above two garage doors. 

Nathan and I posted ideas back and forth. Nathan needed to draw and define the curves, especially how the arc over the shuttered windows evolves into the arc which ends in a point above the main window.

While we focused on that curve I wondered how the master builder laid out the whole design. What geometry might he have used so that the pediment complimented/completed the windows? So it is integral, not just stuck on the top?  

 

 

 

 

 

 

The first task was to see the form that was there: 

A center window flanked by 2 skinny windows, now shuttered. Together with their casings they form a rectangle. The 3 windows' tops are half circles. Around and above them is the embracing molding which follows the semi-circles before it swoops up with a reverse curve to meet at the center in a point. The molding seems to be the same width throughout.  

We saw that the pediment was derived from the windows. The windows and their casings were a rectangle, 4 units wide. Note the red  rectangle and lines below the window sill.  

 

The curve for the section of the pediment over the side windows was easy to see and draw. It's the extension of the small windows' half circles. The red dashed line and the dotted lines drawn here radiate from the center of those shuttered windows. I shared this with Nathan. 

 

The pediment's height over the center window was also easy to find - see the dashed red arc on the right. The half circle's radius is half the width of the windows.  Note the black dashed line. It's a reverse curve. Where was its center? How was it generated?

The white-out on the image comes from us exploring and rejecting options.   

Nathan and I shared ideas back and forth. He posted this suggestion: a layout based on the width divided into 4 units.  

 He extended my 4 units into rectangles, divided the rectangles themselves into 4 parts and used 3 units as the radius for the molding hoods over the shuttered windows. 

The sides of the rectangles cross the semi-circle. He added diagonals from that point to the center of the top of the main window. The crossing point became the center of several exploratory circles for the reverse arc curving to the pediment's center.

 

 

Nathan ended up with this diagram. It worked for the width of the garage doors; he could lay out the curves and cut the parts. 

 
 

 

 

 

I wanted to know about the original design - the layout of windows, casings, pediment with moldings. How might the master builder/ joiner/carver (I don't know his title) have laid out the design? 

 Here's what I saw.  Nathan's division of parts worked across the width of the window. The whole width is 16 parts/units.The center window is 6 parts wide; the casing on each side is 1 part. The side windows are 3 parts wide; with one part on each side for the casing.  

Nathan's geometry for the reverse arc over the main window also worked. The radius of the center window's arched top is 3 parts, with the casing: 4. This doubled is the diameter of the circle which draws the arc of the  pediment.

 

 

   

   

 

 

 

 

 

 

 

The Old First Church Windows in the Lantern

The windows in the lantern of the Old First Church in Bennington, VT, are pretend,  a frame with black paint in between the  muntins. 

This part of the church steeple has a small trap door, 14 ft above the platform, not an easy access. The post which supports the weather vane is in its middle. Repairing broken windows would require scaffolding.

 

 

 

 

 

 

Look up. Does it matter? Would the effect be different with glass? 

 

 

 

 

 

In the 1980's, the church steeple was repaired. In order to replace the rotted frame the lantern was removed. It sat in front of the church for several months. The photograph shows the lantern, suspended from a crane's hook, being lowered onto a base.

 

 Charles Dewey, a local historian and skilled joiner, created  a wood replica of the false windows' layout for the painters. On it he wrote: "SAVE" and  "template for steeple lantern false windows, 1984 restoration". The template is 33" wide x 72" tall.

This pattern is big enough and simple enough to be a clear, final statement at the very top of the steeple, complimenting the 6 columns, their corbels and capitals, and the lantern's curved dome. 

 

What was the geometry?

 The first diagrams are the pattern used for all the windows in the church*.  The circles are laid out on a line. Every time a circles cross the line it makes 2 points which can define a new circle - one on either side here.  

The next circle crosses the original circle at 2 points,  making a vertical line, bisecting a shape with 2 curved sides - a 'vesica piscis' (Latin for 'fish bladder') and give a new point where the new line cross the center line. The new point can become the center for a new circle.

 

The 2nd floor arched windows and the Palladian windows of the church use half of this pattern for their muntins.

 

 

If the whole circle is used it looks like this.

Here is the center half of the pattern. This is the shape of the 6 faux windows.

 

 

 

 

Note that in the diagram above the red arcs cross the underlying circles twice, at the top and bottom. Given 2 points a straight line can be drawn, crossing  the center line, giving a new center for a circle - or here for arcs which outline 4  smaller vesicae piscis.

 

 

The curves at the bottom and the top of the window frame come from the geometry of the church design, As seen here the chains of circles which govern the plans and elevations of the church are both horizontal and vertical.

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Here are the horizontal circles in my first diagram above turned vertically.

 

 

 

 

 The vertical series laid over the horizontal series of circles with the interior muntin pattern shown.

 

 

4 points marked where the horizontal circles cross, allowing connecting lines to be drawn - light dashed vertical lines which mark the edges of the muntins. The points above mark where the vertical circles cross.

 

 

 

Extend the vertical lines and the horizontal lines so they cross.  The points where they cross are the centers for the circles whose circumferences edge the lantern's vesica piscis faux window.

I have not extended the vertical circles nor drawn the lines for the bottom of the window. It is identical to this pattern. 

 

 

 

Those circles, added here in red, form the lower and upper muntins.

If fully drawn and continued they would add  horizontal chains of circles above and below the original center chain and intersecting that chain.

These patterns were difficult to draw accurately by hand at a small scale.  I plan to lay them out again, full scale, on a framing floor to see how easily they come together.

*Links to those blog posts will be added to this post. 

Practical Geometry Lesson 5, Addendum

Why I left out diagram K from Owen Biddle's Plate 1 in his Young Carpenter's Assistant.

Lesson 5 was written for a student today who wants to draw rectangles using practical geometry.
Biddle was writing for the apprentices he worked with in 1805. They needed to know the practical application of geometry for the buildings they worked on - including the curved parts.

This addendum is like one of those long footnotes in an historic report -  a part of the story that's not quite germane to the subject, but ought to be included.


Biddle  identifies each diagram on Plate 1with a letter. There is no diagram for D. However, in his text, between C and E he discusses the mathematical instruments a carpenter should obtain. Perhaps this is D.  I quote him:

- scales of equal parts on the thin ivory or box rule
- a bow pen or compass
- a small piece of gum elastic for rubbing out black lead lines
- a stick of Indian ink
- 2 camel's hair pencils, one large, one small
- a black lead pencil



There is also no J. And there is no text in its place as exists for D. 




Here is K.  

Biddle writes: "Three points (not in a right line) or a small part of a circle being given to find a center which will describe a circle to pass through the points or complete the circle."

                                                     
                                                     Start with a curve a-b .
                                 The curve in Biddle's drawing above is a-b-c.                       










 The curve divided in half:  Swing 2 arcs that are the same length  above above and below the curve: a-c and b-d. Mark where they cross, at f above and below the curve,









Connect  f and f with a line - here dashed. Mark where the line crosses the arc a-b -  I've labeled it g.
This line divides the arc in half. 
If 2 lines were given - here: a-g and g-b , this step would not be necessary. Biddle's diagram  labels his lines a-b and b-c.

Now, the instructions become complex.
Draw it step at a time. And consider that this is only Plate 1 of Biddle's pattern book. He included 43 more Plates for the carpenter's assistant.  

Divide the lines a-g and g-b in half.
This is shown in Biddle's E  and F diagrams. Check Lesson 5. 

Extend the lines which divide  a-g and g-b in half so they intersect at k,
K is the center of the circle which passes the points or completes the circle.

Refer to Biddle's drawing K above for the complete solution, all neatly explained in only one diagram.  



Clearly Biddle thought this information  was essential knowledge for  every carpenter. His next Plates illustrate why. The construction his 'young carpenter's assistant' would be working on involved determining and laying out many curved lines for vaults, arches, windows, stairs and railings.

Plate 2 discusses ellipses: how to draw them using geometry or a trammel, how to find the center and axes of one already drawn.   















Plate 3 is concerned with octagons, arches, groins. the use of trammels, how to divide a line into parts.

I am quite fond of Figure 1, describing " an Octagon within a square." . Simple, quick, even obvious - if you know geometry.

I have seen  painstaking explanations of  how to lay out an octagonal using algebra: quite painful.

Plate 6 reviews raking cornices and "the sweep of a cornice which will bend around a circular wall and stand on a spring."

Plate 31 lays out "the section and elevation of a circular or geometrical stairs". Biddle includes in figure C  "the manner of drawing a bracket for the ends of the circular steps..." and the careful, detailed instructions.




Plates 32-35 - not included here - explain how to layout the newel, the falling moldings, the hand rail for such a stair.






Biddle's Young Carpenter's Assistant, Owen, Biddle, 1805, originally published by Benjamin Johnson, Philadelphia, and Roland and Loudon, New York. Reprint by Dover Publications, Inc. 2006. If you want this book, you can easily order it from them directly. It has an excellent 15 page introduction with bibliography by Bryan Clark Green.

The posts in this series  Lessons 1-7  are :

 https://www.jgrarchitect.com/2020/04/lessons.html

 https://www.jgrarchitect.com/2020/04/practical-geometry-lessons-2.html

 https://www.jgrarchitect.com/2020/04/practical-geometry-lesson-3.html

 https://www.jgrarchitect.com/2020/04/practical-geometry-lesson-4.html

https://www.jgrarchitect.com/2020/04/practical-geometry-lesson-4b-old-first.html

https://www.jgrarchitect.com/2020/06/practical-geometry-lessons-lesson-5.html

https://www.jgrarchitect.com/2020/06/practical-geometry-lesson-5-addendum.html

https://www.jgrarchitect.com/2020/08/lesson-6-rule-of-thirds-part-1_21.html

https://www.jgrarchitect.com/2020/08/lesson-6-rule-of-thirds-part-2-serlio.html

 

https://www.jgrarchitect.com/2020/09/lesson-7-how-to-layout-frame-with-lines.html

"beautiful variety of light and shade"

Asher Benjamin, 1773- 1843  Builder and  Architect

Asher Benjamin wrote for carpenters. He starts The American Builder's Companion with ten plates of basic knowledge a 'joiner' would have needed in the early 1800's, including how to divide a circle, how to layout mouldings.

Many readers seem to skip this technical part of his books, seeing it as archaic. Sometimes historians are interested in how Georgian architecture changed from using mouldings based on the circle (Roman) to those based on the ellipse (Greek). So they note the plates and move on.

They miss the man who knows how light creates. He cares about what he is seeing so passionately that he figures out how to write about it so he can share it with his readers.
I know first hand that it's not easy to put what an architect sees into words that someone else can understand!

Try this:
" In the Roman ovolo there is no turning inward, at the top: therefore, when the sun shines on its surface, it will not be so bright, on its upper edge, as the Grecian ovolo; nor will it cause so beautiful a line of distinction from the other moldings, with which it is combined, when it is in shadow, and when lighted by reflection.
...the Grecian, or quirk ovolo, ... if it is entirely in shadow, but receive a reflected light, the bending, or turning inward, at the top, will cause it to contain a greater quantity of shade in that place, but softened downward around the moulding to the under edge."

As I read his text, I met the man himself.

The quotes are from Plate IX, Names of Mouldings, American Builder's Companion, 1810.

This portrait is from the Dover Publications reprint, 1969, of The American Builder's Companion, Asher Benjamin, 6th edition, 1827. The Public Library in Greenfield was designed by Benjamin.  I have seen the original portrait at Historic Deerfield, Deerfield, MA, where Benjamin built a school.