Because of how moveable type historically developed, typefaces are engineered to be set in horizontal sequence on a straight baseline (except for certain East Asian scripts like Chinese or Mongolian of course). In the 20th century poets, authors and designers discovered other, more expressive ways to arrange typographic matter – just think of avant garde typographic movements like Futurism for example. Setting type on a curve was (and still is) an elaborate task when using physical type in metal or wood, and even with the advent of phototypesetting in the 1950s and ’60s it could only be done on certain systems with distortion filters and anamorphotic lenses. The introduction of graphic design apps like Adobe Illustrator in the mid to late ’80s removed any practical restrictions, making type on curves and in circles a common technique in graphic design.
The principles governing the mechanics of spacing and kerning hinge on the premise that type is set on a straight line. Setting type on a curve distorts the white parts between the letters and changes the predicted outcome. The curved baseline causes the two half spaces between any two glyphs to be arranged at an angle, thus combining to form a space of a different, unexpected shape. While this creates no real issue with some glyphs, other letter pairs produce new spacing problems that could not have been foreseen by the typeface designer. Those need to be corrected by manually adjusting the kerning.
We learned in the two previous episodes that spacing and kerning are built into the fonts. The spacing is an integral part of the glyphs themselves, and the table with the kerning values is saved into the font. Kerning can only work within one single font. So for example a small cap letter will be properly kerned with a lowercase letter if the small caps are part of a feature-rich OpenType font, but not if the small caps are in a separate Expert Set that is part of a legacy TrueType or PostScript font family.
This has important implications when combining different fonts in words. For example you may want to emphasise part of a word by switching that part to italic, or add a decorative capital at the beginning of a word. The ascender or descender of an italic glyph may crash in that of an upright glyph, or the half space to the right of the decorative capital may be incompatible with the half space to the left of the following glyph. Because kerning only works within a font, not across different fonts, you need to correct any occurring spacing problems by manually adjusting the kerning.
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