Sunday, March 31, 2019

A Cabin on Magnolia Plantation, Louisiana

May 14, 2019. I have rewritten this post. The new one is based on being there.
I will leave this one for a while  since so many people have read it. The comparison between  analysis by HABS drawing and an actual site visit is worth noting.  The italicized notes were added as I saw what I had mistaken.

I will be in Natchitoches, Louisiana, April 23- 25, teaching Practical Geometry, in a full day workshop on Thursday, and 2 hr. workshops on Friday and Saturday. 

This image - the cross section of a cabin, built c, 1830, on the Magnolia Plantation, its geometry and a compass - is my on-line poster for the Thursday workshop. It and a description of the workshop is now posted on the Preservation Trades Network website: 

I have the HABS drawings for this cabin, but no picture, as I have not seen yet it.
I hope to visit when I am at the conference.
It's too easy to miss something essential when I work on the geometry of a building I have not be in and around. On the other hand, including local buildings in my workshops and power point talks is important, and researching their geometry will help me see them more clearly when I am there. 

Corn cribs and cabins were utilitarian, built using ordinary construction. Studying these simple structures helps me understand what geometries the local carpenters used.

This cabin has brick walls. It has 2 rooms with back to back fireplaces in the center. The floor plan begins with a square space and its diagonal used as a radius to draw an arc. Then another square space was added on the other side. The space created by the arc is for these fireplaces - possibly including their foundations.  
Follow the  black  line and arc with arrows and the red line and arc with arrows.
This layout is possible. The layout inside the brick wall (see the new post) is simpler and would have easier to to build. 


The section of the cabin shows a floor set above the ground.  The height of the cabin is half the width, here shown by 2 squares, beginning at  grade, not at the floor.  
The diagonals of the squares becomes the radius for arcs; the point where they meet is the cabin's ridge.  Follow the  black  line and arc with arrows and the red line and arc with arrows.

The squares could be moved up; base on floor, top on the rafters. But then the arc would be above the roof line. 

The end elevation matches the section and locates  the window - see arrows.

The side elevation continues the pattern: 2 squares on either side of the center partition, the windows centered on the double square. The red square shows both the partition location, left, and the window location, right. This geometry is not consistent with the construction that I saw. I redrew the elevations.

There are 2 issues I can't resolve without more knowledge of the building and its construction.

1) The window locations on the floor plan do not match those on the end elevation. Which should I use for my analysis?  Most were added later. I can ignore them when I look at the geometry.
Most of the brick houses I have studied use geometry to mark where an opening begins rather than a center line. This is why I think my geometry here is wrong and that in the new post is right.

2) I do not know enough about brick construction in Louisiana to make educated assumptions about framing.
How do the floor and the walls join? Is there a sill?  There seems to be a plate. How is the roof framed? What is the reason the end walls are higher than the sides? Some of this I could not see. People could tell me about details that they had worked on.
The site appears level in the drawing,  with brick footings maybe 18" deep, slightly wider than the walls. Is that the whole foundation? Yes The footings are about 12" deep.
Is there a foundation for the chimney? I did not find out about the chimneys.
All the buildings whose geometry I've analyzed have been no farther south than Virginia. Their geometry begins at the place where a flat base, a foundation, can be set true and level. Where is that here? Has this to do with climate or topography? Topography.

I look forward my visit.

The website for Magnolia Plantation is: 


The NPS has several articles about slavery in Louisiana including this:

The HABS drawings call this a "slave cabin".  I refer to it as a cabin.
The first people who lived here probably were enslaved. They were people first, with skills and families. Maybe their names have been recorded, possibly connected to this cabin. Later free blacks and Creoles lived in these houses at the plantation.
Maybe a mason or a brick maker lived here and I am studying his skill and knowledge.
I have learned that on some plantations tutors and overseers who were not enslaved often  had similar housing. 
This is a "cabin".

Saturday, March 9, 2019

The Geometry of Fences, c. 1830

Asher Benjamin's The Architect or Practical House Carpenter, published in 1830, includes a plate with 3 designs for fashionable fencing,  2 for gates. The lower drawing also includes a post.

While Benjamin includes a scale between the middle and the lower illustrations, he gives no other dimensions or information. He assumes the reader will know how to lay out the design.

The 2 right hand designs are repeated diagonals. quite simple to draw: cross your rectangle, lay in the horizontal and vertical center lines, embellish as you wish.
The bottom drawing is the fence for the gate above and shows the post and its ball.

What about the fence with curved balusters and the gate below it with rectangles and crosses?

First: the fence with curved balusters: 
The center of the rail is the center of the arc. The extended arc becomes a semi-circle  whose radius appears to be the distance to the edge of the bottom rail from the center and the height to the post below the ball and its base.

The arc determines the curve of the baluster. The circle using the same radius, centered on the baluster, follows the reverse curve. Both balusters are shown in red. 
Using Benjamin's scale the balusters could be cut from boards about 3 feet long and 8 inches wide. They are all the same shape.

The circles intersect  - see the vertical dashed lines in black. That intersection gives the spacing for the balusters.
Drawing the next circle using the point where the first circle's circumference crosses the center line, adding the vertical at the intersection, the placement for the balusters, noted in red. continues.

The gate seems at first glance to be more complex.

In my exploration I decided the size and the structure of the gate was known - its width, the framing members, the depth of the bottom rail. The black rectangle outline is what's left - the space for the fret work.
The diagonals are easy to draw - corner to corner. The space can be easily divided in half horizontally and vertically. I have not noted those lines.
But what about the inner rectangle?  The little corner squares?

Two radii are drawn; both A and B are arcs the height of the space, their centers are in the bottom corners, they arc from the top to the bottom - follow A and B's arrows.  They cross at C which is both the vertical center of the rectangle and the depth of the cross brace.

Reverse the arcs.  Now A and B land on the bottom rail  and mark the placement of the vertical braces. C marks the horizontal brace .

The horizontal and vertical braces are noted in red.

The rectangle of the space could be larger or smaller without changing the way the design developed or the general appearance. The proportions would still relate to each other.

The reader in 1830 - probably a house carpenter - would not have required my explanation to copy or adapt the  designs for his own use. He would have learned Practical Geometry as an apprentice. He would have read the design development automatically; he needed no words of explanation.
He might have drawn  his own small diagram on a board. Then he would have drawn the arcs full size on his framing floor - or table, as this is not very big - and found his lengths. The diagram would have remained until all the parts were made.

Plate XXXIII, Asher Benjamin's The Architect or Practical House Carpenter, 1830, L. Coffin, Boston. From the Dover Reprint first published in 1988.

This Asher Benjamin pattern book especially interests me because a diary was written by a local farmer in this period. Its author notes that his friend, a carpenter, traveled twice to Albany to buy his copy of the pattern book when it was first published. The details in several local houses seem to indicate that the joiner worked directly from Benjamin's plates.