Fraction Slash
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Lindsey Hudlow Charles
Posts: 5
Hello,
Working on my second typeface and I'm doing some fractions right now. I've made numerators and denominators, but I was wondering if anyone could shed some light on the fraction slash for a beginner.
The way I had imagined them looking was like this: https://cl.ly/gdtr
But I recognize that in good typefaces, the fraction slash is diagonal, I suppose so that you can type out any long fraction you want.
My question then— is having a horizontal fraction slash something that ever happens—or does it seem to all of you more like a tacky idea to be abandoned?
Working on my second typeface and I'm doing some fractions right now. I've made numerators and denominators, but I was wondering if anyone could shed some light on the fraction slash for a beginner.
The way I had imagined them looking was like this: https://cl.ly/gdtr
But I recognize that in good typefaces, the fraction slash is diagonal, I suppose so that you can type out any long fraction you want.
My question then— is having a horizontal fraction slash something that ever happens—or does it seem to all of you more like a tacky idea to be abandoned?
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Fractions with a horizontal bar instead of a diagonal one are called "en" or "nut" fractions in typography. The more common diagonal bar fraction is called an "em" or "vulgar" fraction. I wouldn't use the horizontal style unless I was designing a font for mathematical or other special use. You could of course include both, although EN fractions are not encoded in Unicode.
3 
The fraction slash should be diagonal, and is used in linear fractions, but it is possible to use OpenType Layout to provide stacked (nut) fractions (typically as a variant form, with the linear form as default). It is even possible, with some caveats, to support arbitrary stacked fractions. See Nutso.6

The separate fraction slash slot should almost certainly have a diagonal bar.
For the precomposed fractions, you are welcome to structure them as you like. Vertically stacked “nut” fractions require smaller numerals and hence are a bit less legible at small text sizes, but they are otherwise a perfectly reasonable design option.
It is even possible to support arbitrary fractions as nut fractions, although the code is rather more complex.2 
Matthew Carter is fond of nut fractions in his fonts. There was a version of ITC Galliard that Carter & Cone distributed back in the day that had an expert set for setting multidigit nut fractions.
Matthew specified that the precomposed fractions in the updated Big Caslon be nut fractions. I proposed developing a {frac} feature that would also provide arbitrary nut fractions. I even produced a proof of concept.
(This was, coincidentally, around the same time John unveiled his Nutso, unknown to me when I first tackled this. My solution was slightly different, not relying upon {mark} for the arbitrary positioning among other things.)
But in the end FB decided not to pursue, mostly because it wouldn’t work in a default InDesign environment since it relies upon the WorldReady Composer (which is sadly not the default).
3 
Correction: The ITC Galliard expert set had only precomposed fractions (half, thirds, quarters, fifths, sixths, and eighths).
It was Carter & Cone’s cut of Monticello that had a “Tabular” font with offset numerators for arbitrary nut fractions. Not sure you can get those forms in the commercial OpenType versions. If you can, I seriously doubt there’s a feature to implement them.
1 
As a graphic designer, a certain amount of quirkiness in a typeface might be just the thing I'm looking for, or it just might be the reason I choose to use another typeface. A horizontal fraction symbol is interesting, but more than likely in most situations, I'd regard it as an attentiondiverting annoyance to be worked around.
If it's an allaround quirky typeface that you're designing, a horizontal fraction just might fit nicely as a natural continuation of the face's personality. On the other hand, if the horizontal fraction really does stand out as an oddity that leaves designers, like me, and readers scratching their collective heads over why it's there, well, that's another matter. If so, maybe including these outoftheordinary fractions as alternates might be your best bet.3 
Interesting. To me, having gone to school in Germany, horizontal fraction bars are the way it «should look», as it is the only way taught in school. The diagonal fractions are the quirky version to me
This is quite typical German math notation:
(also note the 1 with the incredibly long nose and the seven with bar, my upcoming handwriting font has that as a stylistic alternate for German)5 
Thank you, all! This was all very helpful!0

@Jens Kutilek  That would be correct for math notation.
0 
Yes, math notation everywhere uses nut fractions.0

Nut fractions are far less common in nonscientific typographic settings these days. But I suspect they were a bit more common a century ago, in the metal era.
3 
In part that may be because a century ago fonts didn't routinely come in families with weights ranging to extra bold or black (the squeezed Pabst example above notwithstanding).2

I experimented with making arbitrary nut fractions, but there were issues in support from layout applications. It’s easier just to make precomposed fractions that substitute in the Fractions feature (see below).
Lindsey, bear in mind that often the Fraction feature will not be used, so it’s a good idea to make the fraction glyph thin, so that it is matched to your basic lining figures, reduced to 66% size by layout apps (or whatever the default percentage is). And with appropriate sidebearings.
Nut fractions are appropriate for certain kinds of typeface, notably didones, because in this day and age, consistency is expected throughout a type family, and nut fractions are problematic in heavier weights of most other serifed genres, and sans.
Here is a fairly simple code for Fractions:feature frac {# Fractions# Prebuilt stacking fractions, otherwise slashed fractionssub one slash two by onehalf;sub one slash three by onethird;sub one slash four by onequarter;sub one slash eight by oneeighth;sub two slash three by twothirds;sub three slash four by threequarters;sub three slash eight by threeeighths;sub five slash eight by fiveeighths;sub seven slash eight by seveneighths;sub slash by fraction;sub @figs space' [@figs_numr onehalf onethird onequarter oneeighth twothirds threequarters threeeighths fiveeighths seveneighths] by space.frac;Tal Leming has some excellent material on the subject:
} frac;
http://opentypecookbook.com/commontechniques.html
0 
For heavy nut fractions, why not let the numerators and denominators hang over the cap and base lines? Is there any reason that they would need to be so strictly aligned and crushed to fit?5

Some fonts even omit the fraction slash.0

I unearthed this as a walk down memory lane for those of us who worked with Postscript Type 1 expert sets back in the day. ;)
3 
For anyone interested in generating nut fractions easily, below is what I use to generate them. "fracbar" is a horizintal bar component glyph I make that is the midpoint.
fracbar+onesuperior+~fourinferior=onequarter.nut fracbar+onesuperior+~twoinferior=onehalf.nut fracbar+threesuperior+~fourinferior=threequarters.nut fracbar+onesuperior+~threeinferior=onethird.nut fracbar+twosuperior+~threeinferior=twothirds.nut fracbar+onesuperior+~eightinferior=oneeighth.nut fracbar+threesuperior+~eightinferior=threeeighths.nut fracbar+fivesuperior+~eightinferior=fiveeighths.nut fracbar+~sevensuperior+~eightinferior=seveneighths.nut fracbar+onesuperior+~fiveinferior=onefifth.nut fracbar+twosuperior+~fiveinferior=twofifths.nut fracbar+threesuperior+~fiveinferior=threefifths.nut fracbar+foursuperior+~fiveinferior=fourfifths.nut fracbar+zerosuperior+~zeroinferior=zeronut.nut
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