Wednesday, September 10, 2014

Glyph design: the lowercase x





The lowercase ‘x’ is one of those letters that isn’t hard to make, just tedious. The ‘x’, while seemingly simple, requires numerous (but well documented) optical corrections. You also have to consider the negative space in the letter, something you usually only have to think about with round letters like ‘p’ or ‘e’.

The superficial structure of the letter isn’t complicated. It has a single thick diagonal, crossed optically by two arms, collectively called the letter’s hairline, since it is supposed to represent the hairline thickness of the font.

The ‘x’ isn’t a very common letter. The most abundant English letter, ‘e’, is eighty-five times as common. In a typical page of English text, ‘x’ only occurs once every seven hundred letters, on average. Only ‘q’ and ‘z’ are rarer. But the letter is of great interest to typographers, since it stores a a lot of a typeface’s measurements. The height of the letter determines the optical size of the lowercase letters and sets the mean line of the typeface. This is why font size is sometimes expressed in terms of “x-height”, especially when point size is unreliable. The letter’s four corners (including serifs) roughly form a square in a normal style typeface—if it’s wider than it is tall, the font is extended, if it’s significantly narrower, the font is considered condensed. The width of its arms sets a typeface’s hairline thickness, and its hairline compared to the thickness of its diagonal can be used to measure the stroke contrast.
Components of a lowercase ‘x’
Components of a lowercase ‘x’
The diagonal of the letter can be made from the diagonals of two ‘v’s. It is important that the serifs of the ‘v’s align exactly to the baseline and the meanline of typeface, or else you will create an ‘x’ that is too tall or too short, which will be very hard to correct later on. The diagonal should be sheared over so that it spans slightly less than the width of the ‘v’.

Since the shear will reduce the thickness of the diagonal, weight should be tacked back onto the stroke so that it appears the same width as the diagonal in the ‘v’. Weight should be added on the inside of the letter (not the extreme corners), preserving the letter’s width and reducing the optical angle.
The letter’s hairline can be constructed in much the same way. Note that the hairline intersects the diagonal slightly above the letter’s median. This prevents the ‘x’ from looking top heavy.
Because of an optical illusion that makes diagonally crossing lines appear misaligned, the hairline must be broken into two slightly offset arms. The fracture is very slight—anything more than a fraction of a hairline width will make the letter appear misaligned again—this time in the other direction.
Finally, like the ‘v’, there is some radial thickening going on along the arms of the ‘x’. The diagonal can also benefit from some very slight pinching at its intersection point. You might also want to tone down the serif lengths, especially on the inside of the letter to prevent the letter’s crotches from looking closed off. Not all typefaces do this though.