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.
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 (firstname.lastname@example.org)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.