'Gadroon', besides being a lovely word, is a gorgeous Classical moulding, quite sculptural in its form, and thus quite different from the other, more picky mouldings such as Waterleaf or Acanthus.
Don't confuse 'gadrooning' with a name for a similar pattern: 'nulling'. Gadroons curve and have thin and thick ends. 'Nulls' are like lined-up, parallel sausages...
Wood: We'll start with a practise piece as usual before upping the ante into the project. Choose an easy carving wood for the exercises; Jelutong is what I am using here but Limewood (Basswood) would be a good option. For the project itself I used a hard wood, one that polishes well - it's the smooth shiny, marble-like curves that give the gadroon moulding such an attractive appearance. You'll need to plane up a length of blank profile...
Profile: The profile is technically called a 'torus' moulding, the sort you often see at the base of a column. It's the difference in radius between top and bottom edges of the torus that gives the teardrop, curving effect of gadroons.
I've drawn my version in the download (link below) but the gadroon torus really has many variations: shallower, plumper, or the relationships between the top and bottom edges. I'd encourage you to try different profiles and sizes of gadroon so you really see how the thing works. Small gadroons, for example, suit the edge of furniture, such as a table, very well.
Dimensions: Base the download profile on a thickness of 1 1/8in. (30mm) at the maximum point in the curve and the width from fillet to quirk 2 1/2in. (65mm).
Tools: You'll need a V tool, and flat (#3) and medium (#6) gouges that match the size of gadroon you are carving. I used at 1/2 and 3/4in. (14, 20mm) for each sweep for the profile in the download.