Designers Alphabet – C is for …..

is for cyma (Si’ma), a wave or “S” shaped moulding profile. The profile is called a cyma recta when the ends of the profile extend in a horizontal plane and a cyma reversa (or lesbian cymatium) when the profile extends in a vertical plane. Though the curves in a cyma can be configured in an infinite variety of combinations with faster or slower curves i.e. steeper or more gentle curves, it was typical to layout a cyma using 1/6 sections of a circle.

A curve generated using one sixth of a circle has some unique properties. The chord that spans the terminations of the arc is equal to the radius of the circle. It’s also no coincidence that the profiles on hollows and rounds moulding planes generate curved sections that are one sixth of a circle.

Occasionally a designer will desire to make a cyma curve faster, thus more dramatic. Divide the chord into seven parts and use six parts, thus a shorter radius to establish a quicker (steeper curve).

The designer divided the chord into seven parts and then used 6/7 of the chord to swing out and locate a focal point. This results in a slightly more dramatic shadow.

Commercial stock mouldings at the local home center often employ slower curves. My guess it has more to do with the needs of mass production than aesthetics. This wave shaped curve shows up in countless furniture designs beyond it’s use in mouldings, from small elements to the major shapes that make up a form.  If you have an example of an interesting cyma moulding adapted for use in a furniture project or a cyma curve in a furniture design, send me a picture at (georgewalker.design@gmail.com)and I’ll add it to this post.

George R. Walker

Michael Dooley shared this photo of a knife case he built. This form is inspired by the wave shape cyma curve. Infinite possibilities!

Jim Galloway shared this –

This is a blow up showing an entablature that I used on this bookcase and on some other designs. It comes from Georgian Architectural Designs and Details by A. Swan 1757 Dover Pub., plate 44, lower. It is a combination of router and table saw work, though the egg and dart is carved.

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About walkerg

Woodworker and writer
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6 Responses to Designers Alphabet – C is for …..

  1. Chris Bame says:

    Hi George,
    Another great post. I like how you”re making this seem so simple.
    I have always designed my moldings by “eye” for the particular piece. I want to go back to a few of them now and see how close I was to the 1/6 th proportions.
    Thanks Chris Bame

    • walkerg says:

      Chris,
      Thanks for the encouragement. Glad to hear that it’s coming across as practical knowledge you can put to use at your workbench.
      George

  2. raney says:

    George,

    I’m not entirely sure I’m correctly interpreting the instructions for a faster curve. Basically, if I understand the technique – then ‘faster’ in this case would be interpreted as covering more than 60 degrees of arc within the space?

    • walkerg says:

      Raney,
      Yes it is covering more than 60 degrees by shortening the radius. If you wanted to make the radius slightly slower you could stretch your compass to 8/7 of the chord and go the other direction. Either way you are making small tweeks to sneak up on the curve you are after. In the case of mouldings, you want to stay fairly close to the curves generated by hollows and rounds. For the curve on a large tabletop or case piece you might double the chord or triple it, thus incrimentally sneak up on the curve you are after. Also, just going through a drawing exercise and using this method to speed up and slow down curves, really helps your ability to visualize. Should you opt to just draw them freehand it helps to have that picture in the back of your head.

  3. Andrew Adams says:

    George,
    I’ve never been able to differentiate the cyma recta and the cyma reversa. Oh, I’ve seen drawings of them before, but hand me a stick of molding and the best I could do was say “Yeah. That’s some kind of ogee.” Your definitions have helped me think about why I’ve had this problem.

    First a thought experiment to illustrate the difficulty. Take a stick of simple cyma molding (no fillets – nothing but a cyma) and orient it into quadrant III like in your examples. Let’s say it’s a cyma recta. Now flip the stick end for end and rotate it to again occupy the quadrant III orientation. You now have a cyma reversa.

    My conclusion is that a molding is a cyma recta or reversa only in relation to something else. A stick of cyma molding can be either recta or reversa depending on how it’s mounted.

    Your defintions work well for a horizontal molding mounted on a vertical surface. Unfortunately they fall apart for a horizontal molding mounted on a horizontal surface and for a vertical molding mounted on a vertical surface. So I’m going to suggest alternatives that I think will work anywhere. Tell me if I’m all wet.

    A cyma is a cyma recta if the end tails of the curve are substantially perpendiculat to the primary surface on which the molding is mounted. A cyma is cyma reversa if the end tails of the curve are substantially parallel to the primary surface on which the molding is mounted.

    Thank you for running this series and for inadvertantly helping me figure this out.

    Andrew Adams

    • walkerg says:

      Andrew,
      You make an interesting point, most of the definitions between Cyma recta and reversa, fall apart when you begin using the profiles other than on a vertical arangement. Another key for telling them apart (also pertains to vertical configurations), is that a Cyma recta typically is a “crowning or terminating” function. In other words it has a concave section at the top of the profile and provides a distinct shadow line to emphasize a termination. A cyma reversa is often used as a “supporting” function or a brace. It has the convex curve towards the top giving the eye the impression that it is supporting a load. Probably best to not get too hung up on names and instead understand how different shapes impact our perception.

      George

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