Here's a useful article on fractions by Ilene Strizver.

I'm surprised you haven't had one or more type designers responding that they have particularly nice methods, historically accurate all the way back to Manutius, that they use for fraction typesetting, without of course answering your question.

1. Use precomposed Unicode fractions whenever your font has them. Generally you're worse off substituting fonts in this case; if so, go to the next step.
2. If your font has precomposed superior and inferior figures, it probably also has a figure slash. Use all those to construct your fraction (which InDesign etc. will facilitate).
3. If you're really stuck (perhaps you're using a 1990s-era PostScript font), you may just have to use superscripts and subscripts and a regular dash. The colour won't match.
4. It's going to be difficult or impossible to produce a stacked vulgar fraction (numerator, horizontal line, denominator in a single column), so don't even bother.
5. Typeset fractions that are composed merely of a numeral followed by a slash and another numeral (3/4) are to be avoided at nearly all cost. Converting to decimal is less bad in that case (0.75 or .75). But there are some contexts, like Imperial measurements used in building construction, where the fractions are actual iconic units unto themselves (1/8″, 3/4″, 7/8″) and should not be converted to decimal. In that unusual combination of events, just live with crappy typewriter-like “fractions.” (And try to use real inch and foot marks, not curled or fake-italicized apostrophes and quotes.)

Better?

--
Joe Clark
http://joeclark.org/

Fractions (the whole glyph) typically match the height of the lining numbers, so the component numbers would normally be a little less than x-height. The same numbers can be used for superiors and inferiors as well as in precomposed fractions. Stem width of the fraction numbers is a just little less than of the lowercase.

The fractions of this type should ideally be created with a solidus, not a slash. The solidus has a steeper angle, and a different baseline than the common slash.

As well, you want designed inferior/superior numbers, which the type designer will have made somewhat stronger so that they match the base weight of the font. Just using a reduced size numeral will result in a faint, weak-looking character that gives bad type color.

I dislike using old style numerals in fractions, but I have had editors who requested them.

I would recommend putting the "fraction" feature in your fonts.

That way, users can compose any arbitrary fraction they like, simply by typing, eg 17/64, selecting it, and clicking on "fraction" in the OT menu.

A good trick is to use lining small-cap figures as the denominator, and copy-paste these glyphs into your superior figure characters. Then use your superior figures for the numerator. Or you could use inferior figures for the denominator, both on the baseline and below it are legit fraction styles.

The "fraction" feature makes the "numerator" and "denominator" features redundant.

I figured out a way to make arbitrary stacking fractions, but decided it was redundant, as if you need complex fractions like that (eg for ratios such as 400/1000), you will probably be using a math font and math software anyway. So if needed, I just put a few basic stacked fractions in my fonts now -- half, thirds, quarters and eighths. They have specific Unicode values.

Nick, if I read your reply correctly you're saying that the numerator, denominator, superior and small-caps figures could all be the same (size) with just different baselines? So you'd make no difference between the superscript and the fraction numbers?

So, correct me if I'm wrong:
- Create lining inferior and superior numbers. Correct the weight to match the rest of the font, but still keep them a little lighter.
- Put the superior fraction numbers at max. ascender height, or the same hight as the lining numbers.
- Put the inferior fraction numbers on the font baseline.
- Negative space the 'fraction/solidus' so that the superior and inferior numbers fit correctly.
- Superior numbers are positioned higher than caps height to stand out in the text.
- Inferior numbers are positioned below the baseline.
- Fraction/solidus angle is steeper and sinks below the baseline.
- Superior and inferior letters are smaller that the numbers.

I just need a quick and dirty solution for those people who use simple fractions. I'm aware that an editor that needs complex fractions needs a math font. As most people don't need this, I just want to design my fonts in such a way that it works for most moderate users.

Ís there really a typographically correct way to do this, or is it up to the font designer? Does anyone have historical material on this topic?

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