Letterform construction - What is a ductus and what is it for?
If you are trying to design a typeface or maybe practicing your lettering skills, learning about the construction of letterforms is a must... but also quite complex.
I think a good place to start is understanding what a ductus is and how it works. Each character has a reason or history behind the way they look, and with this, the way they are built, and the ductus tells us precisely this.
According to The Typographic Desk Reference the ductus is “the combined elements of speed, angle pressure and type of pen used to form a letter”. I’ve found it is sort of a step-by-step guide that tells you which movements are needed to create a letterform.
Different tools held in a different angle, or used at a different speed or direction can create very different results, that is why studying these ”guides” is important. Once you understand the way a letterform was drawn, you can also understand why they look the way they do, and if certain design elements you might wish to add or delete make sense or not.
For example, when you see the ductus of an uppercase letter A, you can see the direction and angle of the tool that was needed to create each stroke, and that can give you a pretty clear idea why the contrast appears on a certain stem, etc. Speaking on this specific example of a letter A, of course you could make changes like reversing the contrast, adding terminals or whatnot, but the ductus provides you with a starting point on how to construct any given letterform.